It’s both too hot and too cold, has no atmosphere, and is no place to take a vacation—but there is an upside.
It’s hard to say anything positive about the exoplanet LHS 3844b. It’s a wretched place; an alien world that orbits its tiny star in less than half a day. As it’s so close to its red dwarf star, it’s tidally-locked—when one side of the planet is always in baking daylight, the other side is in a perpetual frozen night. Oh, and it doesn’t even have an atmosphere.
Why the heck am I even writing about this unfortunate celestial object?
Well, it might not be our idea of an interstellar getaway, but it is remarkable for two profound reasons: It’s a rare look at the surface conditions of a rocky exoplanet orbiting a distant star, and the very fact that astronomers are confident it doesn’t have an atmosphere is a really big deal.
World of Extremes
Discovered in 2018, LHS 3844b is located nearly 49 light-years away. It has a radius 30 percent larger than Earth and orbits a cool M dwarf star. It was detected by NASA’s newest space-based exoplanet hunter, the Transiting Exoplanet Satellite Survey (TESS); every 11 hours, the world drifts in front of the star, blocking a tiny amount of light (and event known as a “transit”) that can be detected by TESS. As it orbits so close to its host star, it’s glowing bright in infrared radiation, giving the researchers of a new study published in Nature an incredible opportunity.
Using observational data from NASA’s Spitzer space telescope, which views the universe in infrared wavelengths, and as the star is comparatively cool and dim, the researchers could discern how much infrared radiation was being emitted from the exoplanet’s “day” side and calculated that it must be cooking at a temperature of 1,410 degrees Fahrenheit (770 degrees Celsius). On measuring the infrared emissions from the exoplanet’s dark side, they realized that the heat from the day side wasn’t being transported to the night side. On Earth, our atmosphere distributes thermal energy around the globe, ensuring that the night and day sides’ temperature difference isn’t so extreme. LHS 3844b, however, isn’t distributing any of its thermal energy creating a sharp drop-off in temperature between both hemispheres. In other words: no atmosphere!
“The temperature contrast on this planet is about as big as it can possibly be,” said Laura Kreidberg, a researcher at the Harvard and Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and lead author of the new study. “That matches beautifully with our model of a bare rock with no atmosphere.
“We’ve got lots of theories about how planetary atmospheres fare around M dwarfs, but we haven’t been able to study them empirically. Now, with LHS 3844b, we have a terrestrial planet outside our solar system where for the first time we can determine observationally that an atmosphere is not present.”
This exoplanet has about as much atmosphere as the planet Mercury or our Moon, and it shares some other traits too. By measuring the amount of starlight the exoplanet reflects (a characteristic known as “albedo”), Kreidberg’s team also took a stab at understanding its composition.
As the world is “quite dark,” they deduced that it’s very likely that it’s covered in basalt (volcanic rock), the same stuff that we find in the crusts of the Moon and Mercury. “We know that the mare of the Moon are formed by ancient volcanism,” said Renyu Hu, an exoplanet scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., “and we postulate that this might be what has happened on this planet.”
An Atmospheric Problem
Red dwarfs are known to play host to entire systems of exoplanets, including many small rocky worlds of similar dimensions as Earth. Many of these worlds have been found within the much-hyped “habitable zone”, where it’s neither too hot or too cold for liquid water to persist. As we probably are all aware, liquid water is super helpful for life (on our planet, at least) to evolve. While LHS 3844b could never be considered “habitable” in any way, shape or form, the fact that it doesn’t have an atmosphere may be very revealing.
It’s simply not good enough to find a habitable zone exoplanet that orbits a red dwarf and say “there’s a good chance that aliens live there!” Even though it has the right temperature, because it’s orbiting a red dwarf and likely tidally-locked could mean these types of worlds are devoid of atmospheres, a serious wrench in the hope that all habitable zone exoplanets have the same likelihood of life. That’s not to say all red dwarf-orbiting exoplanets lack atmospheres, but now at least we are developing techniques that could, one day, help us from the atmospheric potential of more “habitable” candidates.
Who doesn’t love the moon? You just have to look up when the skies are clear and there it is, our lunar friend, doing its thing, changing phases, yanking at our oceans, inspiring the world to look “up.”
It’s little wonder, then, that humanity has created many different names for our planet’s tidal partner in crime. There are useful astronomical names that describe its different phases (new/full, first/third quarter, waxing/waning crescent/gibbous), but there’s also other names that have popped up throughout human history that relate to other subtleties in the lunar dance around our world. A quasi-rare second full moon of the month? Blue moon! When the full moon coincides with perigee (lunar close approach with Earth)? Supermoon! When you get a bonus lunar combo that includes a full moon, a supermoon… and the Earth is blocking the sun so we have a lunar eclipse… and it all happens to occur in January?? That’s a SUPER BLOOD WOLF MOON ECLIPSE!Because of course it is.
As you may or may not have realized, humans—particularly humans in marketing departments, the media, and astrologers with too much time on their hands—like to label things. Some of these labels can be useful, others not so much. Many are, frankly, just plain silly. Which brings me to today’s lunar branding non-event: The Black Moon. Ohh sounds… eerie.
As one who has been involved in the broadcasting field for nearly 40 years, I’d like to point out that we live in a time when the news media is seemingly obsessed with “branding.” This marketing strategy involves creating a differentiated name and image — often using a tagline — in order to establish a presence in people’s mind. In recent years in the field of astronomy, for example, we’ve seen annular eclipses — those cases when the moon is too small to completely cover the disk of the sun — become branded as “Ring of Fire” eclipses. A total eclipse of the moon — when the moon’s plunge through the Earth’s shadow causes the satellite to turn a coppery red color — is now referred to as a “Blood Moon.”
When a full moon is also passing through that part of its orbit that brings it closest to Earth — perigee — we now brand that circumstance as a supermoon. That term was actually conjured up by an astrologer back in 1979 but quite suddenly became a very popular media brand after an exceptionally close approach of a full moon to Earth in March 2011. It surprises me that even NASA now endorses the term, although it seems to me the astronomical community in general shies away from designating any perigee full moon as “super.”
Then there is Blue Moon. This moniker came about because a writer for Sky & Telescope Magazine misinterpreted an arcane definition given by a now-defunct New England Almanac for when a full moon is branded “blue,” and instead incorrectly reasoned that in a month with two full moons, the second is called a Blue Moon. That was a brand that quietly went unnoticed for some 40 years, until a syndicated radio show promoted the term in the 1980s and it then went viral. So now, even though the second full moon in a month is not the original definition for a Blue Moon, in popular culture we now automatically associate the second full moon in a calendar month with a Blue Moon.
So are you ready for yet another lunar brand? The newest one is Black Moon.
That’s a very polite way of saying, “it’s all bullshit, really.”
So, what IS a Black Moon? Well, it’s the opposite of a Blue Moon, as in it’s the second New Moon in the month of July and a New Moon is when the sun, moon and Earth are in almost exact alignment; the entire Earth-facing side of the moon is in complete shadow. The upshot is you can’t see it. It’s a naked-eye astronomical non-event.
Having said that, should the moon exactly line up with the sun, you get a solar eclipse—arguably the most mind-blowing astronomical event we can see on Earth. A plain ol’ Black Moon? Not so much.
UPDATE: As this post turned into the seed for a fun little online discussion, I added some thoughts in the following Twitter thread. Feel free to @ me:
The pair of white dwarf stars are orbiting one another every seven minutes—and future gravitational wave observatories will be able to detect them whirl.
White dwarf binaries are among some of the most fascinating star systems known, and a newly discovered compact binary, located some 8,000 light-years away in the constellation Boötes, has taken the exotic nature of these systems to new spacetime-warping extremes.
Astronomers using Caltech’s Zwicky Transient Facility (ZTF), a precision sky survey at Palomar Observatory near San Diego in Southern California, made the discovery of ZTF J1530+5027 by detecting the dimming effect caused by one of the stars passing in front of the other. Known as an “eclipsing binary,” the cooler (and therefor dimmer) white dwarf blocks the starlight of the hotter (and brighter) star, causing the ZTF to register a periodic dimming event. This dimming occurs once every seven minutes, meaning they are zipping around each other at speeds of hundreds of miles per second! It is the second fastest white dwarf binary known and the most rapid eclipsing binary discovered in our galaxy. The fortunate alignment allows astronomers to not only precisely measure their orbital speed, they can also gauge the stars’ sizes and masses.
White dwarfs are the stellar corpses of sun-like stars that ran out of fuel long ago. Our sun will become a white dwarf in around five billion years, after it has exhausted its hydrogen fuel that maintains fusion in its core. A short period after, it will swell into a red giant (possibly expanding out as far as Earth, incinerating it) and then lose its plasma to space via powerful solar winds. All that will be left of our once glorious star will be a planetary nebula and a tiny and dense white dwarf, approximately the size of our planet, spinning in the middle. The two white dwarfs in ZTF J1530+5027 likely passed through their red giant phase at different times, but now they’re stuck, in a perpetual death spiral that spells doom for one of the objects.
To fully realize just how crazy-extreme this white dwarf binary is, they are only separated by one-fifth of the distance that the moon orbits Earth, meaning both stars would fully fit inside Saturn. They have a combined mass of our entire sun. As they orbit so snugly, it’s likely that the more massive star will start to tidally drag material from the other, cannibalizing it.
“Matter is getting ready to spill off of the bigger and lighter white dwarf onto the smaller and heavier one, which will eventually completely subsume its lighter companion,” said Kevin Burdge, Caltech graduate student and lead author of a study published in the journal Nature. “We’ve seen many examples of a type of system where one white dwarf has been mostly cannibalized by its companion, but we rarely catch these systems as they are still merging like this one.”
While impressive, the real fireworks are invisible—the stars are ripping up spacetime, generating gravitational waves that are sapping energy from the system, hastening the binary’s ultimate demise. What’s more, astronomers are anticipating that the future Laser Interferometer Space Antenna (LISA), which is scheduled for launch by the European Space Agency in 2034, will be able to detect its gravitational pulse.
“These two white dwarfs are merging because they are emitting gravitational waves,” added collaborator Tom Prince, a senior research scientist at Caltech and NASA’s Jet Propulsion Laboratory (JPL, in Pasadena, Calif. “Within a week of LISA turning on, it should pick up the gravitational waves from this system. LISA will find tens of thousands of binary systems in our galaxy like this one, but so far we only know of a few. And this binary-star system is one of the best characterized yet due to its eclipsing nature.”
This system is expected to keep blinking from our perspective for another hundred thousand years, but how will the system ultimately go kaput? Well, the researchers aren’t entirely certain. On the one hand, the more massive white dwarf may suck the other dry like a vampiric parasite, consuming all of its matter until only one, well-fed star remains. Alternatively, the act of cannibalization may cause the reverse; as mass is transferred to one star, the other may be flung outward to a wider orbit, increasing their orbital period.
“Sometimes these binary white dwarfs merge into one star, and other times the orbit widens as the lighter white dwarf is gradually shredded by the heavier one,” said co-author Jim Fuller, an assistant professor at Caltech. “We’re not sure what will happen in this case, but finding more such systems will tell us how often these stars survive their close encounters.”
One early mystery about this extreme binary is the question of X-rays, or lack thereof. The more massive star is really hot, with a temperature nine times that of the sun (50,000 Kelvin). The researchers believe that this is because it has already begun pulling material from its partner, an act that accelerates and heats the plasma that is being stolen, starting to create an accretion disk. But the accreting gas should be so hot that the system would be humming in X-rays, but it isn’t. “It’s strange that we aren’t seeing X-rays in this system. One possibility is that the accretion spots on the white dwarf—the areas the material is falling on—are bigger than what is typical, and this could result in the emission of ultraviolet light and optical light instead of X-rays,” added Burdge.
It’s exciting to think what the next generation of gravitational wave observatories (particularly LISA that will be sensitive to extremely weak spacetime ripples from systems such as these) combined with traditional (re: electromagnetic) observatories will herald for the future of astronomy. Like the emerging “multi-messenger” era for astronomy that combines observations of the electromagnetic spectrum and gravitational wave signals to confirm short gamma-ray bursts are triggered by neutron star collisions, it’s going to blow our minds when we can access more subtle gravitational wave sources such as these and directly see the gravitational energy leaking from compact binaries.
An international team of experts have teamed up to conclude that the interstellar visitor isn’t what we hoped it was.
It probably comes as no surprise that the scientific consensus of ‘Oumuamua’s origins have concluded that it is a natural object, despite how funky and alien spaceship-looking the interstellar visitor at first appeared. According to a new study published today in the journal Nature Astronomy, the findings of 14 international experts have been pooled to categorically say that ‘Oumuamua isn’t an artificial object piloted by an intelligent extraterrestrial species, but instead “has a purely natural origin.”
“The alien spacecraft hypothesis is a fun idea, but our analysis suggests there is a whole host of natural phenomena that could explain it,” said the team’s leader Matthew Knight, from the University of Maryland, in a statement.
This most recent study comes hot on the heels of a fair amount of speculation that the spinning cigar-shaped object, which was detected by the Pan-STARRS1 telescope in Hawaii on Oct. 19, 2017, could be artificial. One of the more vocal advocates of this possibility, Avi Loeb of Harvard University, investigated the idea that ‘Oumuamua may be an interstellar probe that used our sun’s radiation pressure for a boost in velocity as it flew through the inner solar system. While the world’s media loved this concept (as did I), many scientists balked and emphasized the need to take the Occam’s razor approach and instead focus on natural explanations, not aliens. But, as pointed out by Loeb, while more likely explanations existed, considering the most extreme ones is still a part of the scientific process.
“This is how science works,” said Loeb in an interview for The Harvard Gazette late last year. “We make a conjecture … and if someone else advances another explanation, we will compare notes and the next time we see an object of this type we will hopefully be able to tell the difference. That’s the process by which science makes progress.”
Deep down, we all had the sense that the interstellar visitor likely wasn’t aliens (though it did spawn some wonderful debates about mind-boggling interstellar distances, the challenges of visiting other star systems, and why ET would bother popping by for a whistle-stop tour without saying “hi”), but this new study convincingly sounds the death knell for the possibility of aliens taking a joyride through our galactic neighborhood.
The new study is clear, in which the researchers write: “Here we review our knowledge and find that in all cases, the observations are consistent with a purely natural origin for ‘Oumuamua.”
So, what does the study conclude?
The object is most likely an ancient interstellar comet that randomly encountered our solar system after drifting through interstellar space for millions of years. The mechanisms by which ‘Oumuamua was ejected from its star system of birth remains up for debate, but the study’s authors point to the likelihood of a Jupiter-like world that may have gravitationally ejected the object when it strayed too close, helping it achieve escape velocity and a future lost deep in the interstellar expanse—until it encountered our solar system.
Even the behavior of the ancient comet as it traveled through the inner solar system agrees with theoretical predictions. The small boost in velocity as it made close approach to our sun was caused by ices (entombed under ‘Oumuamua’s surface) being heated and vented into space as a vapor (and not aliens hitting the gas). This behavior in comets is well-known, but the problem with ‘Oumuamua is that it exhibited few signs of being a comet—it didn’t develop a tail nor did it develop a coma, two clues of its cometary nature. But this object is different from the comets we know; it has been drifting through the galaxy for eons, perhaps it lost the majority of its ice in previous stellar encounters, or perhaps it contained little in the way of volatiles during its formation. Comets and asteroids also have a lot more in common that the textbooks may tell us, so perhaps it did vent small quantities of vapor to give it a boost, but not enough for astronomers to observe a tail and coma. In short, ‘Oumuamua shares similar traits to other objects that exist in our solar system
“While ‘Oumuamua’s interstellar origin makes it unique, many of its other properties are perfectly consistent with objects in our own solar system,” added Robert Jedicke of the University of Hawai’i’s Institute for Astronomy (IfA) and collaborator in the Nature Astronomy study.
The key thing that makes ‘Oumuamua so captivating, however, is not how it behaved when it entered the solar system and used the sun to change its course, it’s that we know it came from interstellar space, the first of its kind that we’ve ever encountered. Undoubtedly, the solar system has been visited countless times by junk that has been shed by other stars in our galaxy—there’s a lot of stars carrying around a lot of comets and asteroids, after all, they’re probably scattered around the Milky Way like baby’s toys being thrown out of strollers—but this is the first, special interstellar visitor that we’ve only just had the ability to detect.
The best news? There will be more.
Humanity is rapidly advancing through a “golden age” for astronomy and, if these interstellar vagabonds are as common as we now believe, we’re on the verge of detecting many more of them. For example, the Large Synoptic Survey Telescope (LSST), which is being constructed in Chile, is expected to become operational in 2022 and it will be so powerful that astronomers predict at least one ‘Oumuamua-like object will be spotted per year. Once we grasp how often these things turn up, perhaps we’ll be prepared enough to have a robotic spacecraft intercept one to see what these visitors from other stars really look like instead of depending on distant observations.
Of course, this whole episode could be a cautionary tale. Perhaps our advanced alien neighbors disguise their spacecraft to look like passing comets to get a closer look of primitive intelligences such as ourselves.* ‘Oumuamua being identified as an interstellar comet is exactly what they want us to believe…
*This was inspired by a tweet I read this morning, but I forgot who tweeted it and it appears I didn’t “like” it, so it’s since been lost to the twitterverse. Thank you to whomever tweeted it, it formed the seed to this blog!
While it’s an exciting discovery, the nearby star system is a very alien place with its own unique array of challenges.
The universe is stranger than we can imagine, so when a star system is discovered with some familiar traits to ours, it can be hard not to imagine extraterrestrial lifeforms and interstellar getaways. But before you dream of bathing on the exotic shores of Teegarden b, breathing in the moist and salty air, while sipping on a Teegarden Tequila Sunrise, keep in mind that the reality will likely be, well, much stranger than we can imagine.
All of these facts are cause for celebration, no? They are, but a heavy dose of reality needs to be applied when it comes to any world that has been discovered beyond our solar system.
More Exoplanets, More Possibilities
As alien planet-hunting missions continue to add more worlds to the vast menagerie of known exoplanets that exist in our galaxy, an increasing number of them are falling inside the “habitable zone” category.
The habitable zone around any star is the distance at which a rocky planet can orbit where it’s neither too hot or too cold for liquid water to exist on its surface (if it has water, that is). Liquid water is the stuff that Earth-like biology has an affinity to; without it, life on Earth wouldn’t have evolved. So, even before we have any clue about its H2O-ness, if an exoplanet is seen to have an orbit around its star that is deemed habitable, that’s +1 point for habitability.
Now, the next point can only be won if that world is also of approximate Earth-like size and/or mass. There would be little reason in getting too excited for a Jupiter-sized exoplanet sitting in the habitable zone possessing liquid water on its “surface” (because it won’t have a surface). That’s not to say there can’t be some gas giant-dwelling balloon-like alien living in there, but we’re looking for Earth-like qualities, not awesome alien qualities we read in science fiction. (I’d also argue that these kinds of exoplanets might have habitable Earth-sized moons—like Avatar‘s Pandora—but that’s for another article…)
The two key methods for exoplanet detection is the “radial velocity” method and the “transit” method. The former—which precisely measures a star’s light to detect tiny stellar wobbles as an exoplanet gravitationally “tugs” at it as it orbits—can deduce the exoplanet’s mass, thereby revealing whether or not it has an Earth-like mass (Teegarden’s two worlds were discovered using this method). The latter—which was employed by NASA’s Kepler space telescope (and now NASA’s Transiting Exoplanet Survey Explorer, among others) to look for the slight dips in brightness as an exoplanet passes in front of its star—can deduce the exoplanet’s physical size, thereby revealing whether or not it has an Earth-like size. Should a habitable zone exoplanet possess either one of these Earth-like qualities, or both (if both methods are used on a target star), that’s another +1 point for its habitability.
There’s a few other measurements that astronomers can make that may add to a hypothetical world’s habitability (such as observations of the host star’s flaring activity, age, or some other derived measurement), but until we develop more powerful observatories on Earth and in space, there are several factors that quickly cause our hypothetical exoplanet to diminish in habitable potential.
The Unhabitability of “Habitable” Worlds
So far in our burgeoning age of exoplanetary studies, we’ve only been able to measure (and derive) a handful of characteristics—such as mass, orbital period, physical size, density—but we have very little idea about these habitable zone exoplanets’ atmospheres. Apart from measurements of a few massive and extreme exoplanets—such as “hot-Jupiters” and exoplanets getting blow-torched by their star when they venture too close—astronomers haven’t been able to directly measure the existence of any of these “habitable” exoplanet’s hypothetical atmospheres. Do they even possess atmospheres? Or are they the opposite, with hellish Venus-like pressure-cooker atmospheres? Who knows. Even if they do have atmospheres that are more Earth-like, are the gases they contain toxic to life as we know it?
Recently, theoretical models of exoplanetary atmospheres brought carbon dioxide and carbon monoxide into the discussion. CO2 is a powerful greenhouse gas that helps maintain a balance in our atmosphere, regulating a temperate world (until industrialized humans came along, that is). But too much can be a very bad thing. For exoplanets existing on the outer edge of their habitable zone to remain habitable, they’d need massive concentrations of CO2 to remain temperate—concentrations that would render the atmosphere toxic (to complex lifeforms, at least). In the case of carbon monoxide (the terrible gas that asphyxiates anything with a cardiovascular system), as our star is so hot and bright, its ultraviolet radiation destroys large accumulations of CO in Earth’s atmosphere. But for habitable zone exoplanets that orbit cool red dwarf stars (like Teegarden), huge concentrations of CO may accumulate and snuff-out life before it has the opportunity to evolve beyond a germ. These two factors are a big negative against life as we know it, shrinking the effective habitable zone around certain stars and certain exoplanetary orbits.
Most habitable zone exoplanets have been found orbiting red dwarfs, primarily because our observations have been biased in favor of these little stars—they’re small and cool, meaning that any planet orbiting within their habitable zones need to get up-close and personal, so it’s an easier task to detect the periodic star wobbles or exoplanetary transits to confirm their existence.
While this may sound cute, orbiting so close to a red dwarf is a blessing (for astronomers) and a curse (for any unfortunate aliens). Many red dwarf stars generate powerful stellar flares that would regularly bombard nearby worlds with radiation that terrestrial biology would not be able to tolerate. Unless those planets have incredibly powerful global magnetic fields to, a) protect their inhabitants from being irradiated and, b) prevent the savage stellar winds from stripping away their protective atmospheres, there’s limited hope for the evolution of life.
Interestingly, however, according to the Teegarden study published in the journal Astronomy & Astrophysics, this particular red dwarf is relatively quiet on the life-killing flare front, so that’s something. Another tentative +1 for Teegarden’s actual habitability!(Pass the tequila.)
As you can tell, there’s lots of exciting implications balanced by plenty of sobering reality checks. There is, however, one factor that is often missed from big announcements about worlds orbiting small stars that, whether they are habitable or not, is truly beyond our experience.
Eyeballing Temperate Red Dwarf Systems
Teegarden is an eight-billion-year-old star system, approximately twice the age of our solar system. If life has found a way, it will have come and gone, or be in an evolved state (though this is anyone’s guess, we have little idea about the hows and whys of the emergence of life on Earth, let alone on a different planet). But the worlds themselves, if either possess liquid water (Teegarden b, being the one that should be the most temperate of the pair, so will have the higher odds), they certainly wouldn’t look like Earth, even if they have Earth-like qualities.
Having settled billions of years ago, any orbital instabilities would have ebbed, and the planetary orbits would be clearly defined and likely in some kind of resonance with the other bodies in the star system. In addition, both Teegarden b and c will, in all likelihood, be tidally locked with their star.
To understand what this means, we need only look up. When we see our moon, we only see one hemisphere—the “near side”; the lunar “far side” is never in view. Except for the Apollo astronauts, no human has ever seen the moon’s far side with their own eyes. That’s because the moon’s rotation period (28 days) exactly matches its orbital period (28 days) around the Earth. Other examples of tidally-locked systems in the solar system are Pluto and its largest moon Charon, Mars and both its moons Phobos and Diemos, plus a whole host of moons orbiting Jupiter, Saturn, Uranus and Neptune.
The same tidal physics applies to red dwarf stars and their closely-orbiting worlds. And Teegarden b and c have very close orbits, zipping around the star once every five and eleven days, respectively, so they are very likely tidally locked, too.
So what does a habitable zone exoplanet orbiting a red dwarf star look like? Enter the “Eyeball Earth” exoplanet:
I’ve written about this hypothetical world before and it fascinates me. As temperate exoplanets orbit red dwarfs so snugly, and if they have an atmosphere, they may too look like the above artistic rendering.
Looking like an eyeball, the star-facing hemisphere of the planet will be perpetually in daylight, whereas the opposite side will be in perpetual night. The near-side will likely be an arid desert, but the far side will be frozen. Computer simulations of the atmospheric dynamics of such a world are fascinating and well worth the read. The upshot, however, is that these worlds may have dynamic atmospheres where habitability is regulated by powerful winds that blast from the star-facing hemisphere to the night-side, transporting water vapor in a surprisingly complex manner. These worlds will never be fully-habitable, but they may host in interesting array of biological opportunities nonetheless.
For example, there may be a “ring ocean” that separates the desert from the ice, where, on one side, tributaries flow into the hot hemisphere only to be evaporated by the incessant solar heating. The vapor is then transported anti-star-ward, only to be deposited as it freezes on the night-side. One could imagine this massive buildup of ice on the planets night-side as an hemisphere-wide glacier that slowly creeps sun-ward, where it melts and pools into a temperate ring ocean where the process starts all over again.
Like Earth, the atmospheric dynamics would need to be balanced perfectly and if an alien ecosystem manages to get a foothold, perhaps such a planet-wide “water cycle” could be sustained while maintaining the life that thrives within.
So, whenever we hear about the latest exoplanetary discovery, and take note that these strange new worlds are “Earth-like” or “habitable,” it’s worth remembering that neither may be accurate. Sure, finding an Earth-sized world in orbit around their star in the habitable zone is a great place to start, but it’s just that, a start. What about its atmosphere? Does it have the right blend of atmospheric gases? Is it toxic? Does it even have an atmosphere? Whether or not an alien world has a global magnetic field could make or break its habitable potential. Does its star have sporadic temper tantrums, dousing any local planets with a terrible radiation storm?
These challenges are no stranger to the astronomers who find these worlds and speculate on their astrobiological potential, but in the excitement that proceeds the discovery of “Earth-like” and “habitable” exoplanets, the headlines are often blind to the mechanics of what really makes a world habitable. The next step will be to directly observe the atmospheres of habitable exoplanets, a feat that may be within reach when NASA’s James Webb Space Telescope (JWST) and the ESO’s Extremely Large Telescope (ELT) go online.
The fact is, we know of only ONE habitable world, all the others are hypothetically habitable—so let’s look after this one while it can still sustain the rich and diverse ecosystem we all too often take for granted.
Don’t forget your spacesuit: Complex lifeforms, such as humans, would not survive on many of the worlds we thought would be interstellar tropical getaways
Worlds like Earth may be even rarer than we thought.
We live on a planet that provides the perfect balance of ingredients to support a vast ecosystem. This amazing world orbits the Sun at just the right distance where water can exist in a liquid state—a substance that, as we all know, is an essential component for our biology to function. Earth is also an oddball in our solar system, being the only planet where these vast oceans of liquid water persist on its surface, all enshrouded in a thick atmosphere that provides the stage for a complex global interplay of chemical and biological cycles that, before we industrialized humans came along, has supported billions of years of uninterrupted evolution and biological diversity.
Humans, being the proud intelligent beings that we profess to be, are stress-testing this delicate balance by pumping an unending supply of carbon dioxide into the atmosphere. Being a potent greenhouse gas, we’re currently living through a new epoch in our planet’s biological history where an exponential increase in CO2 is being closely followed by an increase in global average temperatures. We are, in effect, altering Earth’s habitability. Well done, humans!
While this trend is a clear threat to the sustainability of our biosphere, spare a thought for other “habitable” worlds that may appear to have all the right stuff for complex lifeforms to evolve, but toxic levels of the very chemicals that keep these worlds habitable has curtailed the possibility of complex life from gaining a foothold.
Welcome to the Not-So-Habitable Zone
Habitable zone exoplanets are the Gold Standard for exoplanet-hunters and astrobiologists alike. Finding a distant alien world within this zone—a region surrounding any star where it’s not too hot and not too cold for water to exist on its surface, a region also known as the “Goldilocks Zone” for obvious reasons—spawns a host of questions that our most advanced telescopes in space and on the ground try to answer: Is that exoplanet Earth-sized? Does it have an atmosphere? What kind of star is it orbiting? Does its system possess a Jupiter-like gas giant? These questions are all trying to help us understand whether that world has the Earthly qualities that could support hypothetical extraterrestrial life.
(Of course, there’s the debate as to whether all life in the universe is Earth-life-like, but as we’re the only biological examples that we know of in the entire galaxy, it’s the best place to start when pondering what biological similarities extraterrestrial life may have to us.)
The habitable zone for exoplanets is a little more complicated than simply the distance at which they orbit their host stars, however. Greenhouse gases, such as carbon dioxide, can extend the area of a star’s habitable zone. For example: If an atmosphere-less planet orbits beyond the outermost edge of its habitable zone, the water it has on its surface will remain in a solid, frozen state. Now, give that planet an atmosphere laced with greenhouse gases and its surface may become warm enough to maintain the water in a liquid state, thereby boosting its habitable potential.
But how much is too much of a good thing? And how might this determination impact our hunt for truly habitable worlds beyond our own?
In a new study published in the Astrophysical Journal, researchers have taken another look at the much-coveted habitable zone exoplanets to find that, while some of the atmospheric gases are essential to maintain a temperature balance, should there be too much of the stuff keeping some of those worlds at a habitable temperature, their toxicity could curtail any lifeforms more complex than a single-celled microbe from evolving.
“This is the first time the physiological limits of life on Earth have been considered to predict the distribution of complex life elsewhere in the universe,” said Timothy Lyons, of the University of California, Riverside, and director of the Alternative Earths Astrobiology Center.
“Imagine a ‘habitable zone for complex life’ defined as a safe zone where it would be plausible to support rich ecosystems like we find on Earth today,” he said in a statement. “Our results indicate that complex ecosystems like ours cannot exist in most regions of the habitable zone as traditionally defined.”
Carbon dioxide is an essential component of our ecosystem, particularly as it’s a greenhouse gas. Acting like an insulator, CO2 absorbs energy from the Sun and heats our atmosphere. When in balance, it stops too much energy from being radiated back out into space, thereby preventing our planet from being turned into a snowball. Levels of CO2 have ebbed and flowed throughout the biological history of our planet and it has always been a minor component of atmospheric gases, but its greenhouse effect (i.e. the atmospheric heating effect) is extremely potent and the human-driven 400+ppm levels are causing dramatic climate changes that modern biological systems haven’t experienced for millions of years. That said, the CO2 levels required to keep some “habitable” exoplanets in a warm enough state would need to be a lot more concentrated than the current terrestrial levels, potentially making their atmospheres toxic.
“To sustain liquid water at the outer edge of the conventional habitable zone, a planet would need tens of thousands of times more carbon dioxide than Earth has today,” said lead author Edward Schwieterman, of the NASA Astrobiology Institute. “That’s far beyond the levels known to be toxic to human and animal life on Earth.”
From their computer simulations, to keep CO2 at acceptable non-toxic levels, while maintaining planetary habitability, the researchers realized that for simple animal life to survive, the habitable zone will shrink to no more than half of the traditional habitable zone. For more complex lifeforms—like humans—to survive, that zone will shrink even more, to less than one third. In other words, to strike the right balance between keeping a hypothetical planet warm enough, but not succumbing to CO2 toxicity, the more complex the lifeform, the more compact the habitable zone.
This issue doesn’t stop with CO2. Carbon monoxide (CO) doesn’t exist at toxic levels in Earth’s atmosphere as our hot and bright Sun drives chemical reactions that remove dangerous levels of the molecule. But for exoplanets orbiting cooler stars that emit lower levels of ultraviolet radiation, such as those that orbit red dwarf stars (re: Proxima Centauri and TRAPPIST-1), dangerous levels of this gas can accumulate. Interestingly, though CO is a very well-known toxic gas that prevents animal blood from carrying oxygen around the body, it is harmless to microbes on Earth. So it may be that habitable zone exoplanets orbiting red dwarfs could be a microbial heaven, but an asphyxiation hell for more complex lifeforms that have cardiovascular systems.
While it could be argued that life finds a way—extraterrestrial organisms may have evolved into more complex states after adapting to their environments, thereby circumventing the problems complex terrestrial life has with CO2 and CO—if we are to find a truly “Earth-like” habitable world that could support human biology, these factors need to be considered before declaring an exoplanet habitable. And, besides, we might want to make the interstellar journey to one of these alien destinations in the distant future; it would be nice to chill on an extraterrestrial beach without having to wear a spacesuit.
“Our discoveries provide one way to decide which of these myriad planets we should observe in more detail,” said Christopher Reinhard, of the Georgia Institute of Technology and co-leader of the Alternative Earths team. “We could identify otherwise habitable planets with carbon dioxide or carbon monoxide levels that are likely too high to support complex life.”
Earth: Unique, Precious
Like many astronomical and astrobiological studies, our ongoing quest to explore strange, new (and habitable) worlds has inevitably led back to our home and the relationship we have with our delicate ecosystem.
“I think showing how rare and special our planet is only enhances the case for protecting it,” Schwieterman said. “As far as we know, Earth is the only planet in the universe that can sustain human life.”
So, before we test the breaking point of our atmosphere’s sustainability, perhaps we should consider our own existential habitability before its too late to repair the damage of carbon dioxide emissions. That’s the only way that we, as complex (and allegedly intelligent) lifeforms, can continue to ask the biggest questions of our rich and mysterious universe.
The world’s most powerful radio telescope is getting intimate with Sagittarius A*, revealing a never-before-seen component of its accretion flow
As we patiently wait for the first direct image of the event horizon surrounding the supermassive black hole living in the core of our galaxy some 25,000 light-years away, the Atacama Millimeter/submillimeter Array (ALMA) has been busy checking out a previously unseen component of Sagittarius A*’s accretion flow.
Whereas the Event Horizon Telescope (EHT) will soon deliver the first image of our supermassive black hole’s event horizon, ALMA’s attention has recently been on a cool flow of gas that is orbiting just outside the event horizon, before being consumed. (The EHT delivered its first historic image on April 10, not of the supermassive black hole in our galaxy, but of the gargantuan six-billion solar mass monster in the heart of the giant elliptical galaxy, Messier 87, 50 million light-years away.)
While this may not grab the headlines like the EHT’s first image (of which ALMA played a key role), it remains a huge mystery as to how supermassive black holes pile on so much mass and how they consume the matter surrounding them. So, by zooming in on the reservoir of material that accumulates near Sagittarius A* (or Sgr A*), astronomers can glean new insights as to how supermassive black holes get so, well, massive, and how their growth relates to galactic evolution.
While Sgr A* isn’t the most active of black holes, it is feeding off limited rations of interstellar matter. It gets its sustenance from a disk of plasma, called an accretion disk, starting immediately outside its event horizon—the point at which nothing, not even light, can escape a black hole’s gravitational grasp—and ending a few tenths of a light-year beyond. The tenuous, yet extremely hot plasma (with searing temperatures of up to 10 million degrees Kelvin) close to the black hole has been well studied by astronomers as these gases generate powerful X-ray radiation that can be studied by space-based X-ray observatories, like NASA’s Chandra. However, the flow of this plasma is roughly spherical and doesn’t appear to be rotating around the black hole as an accretion disk should.
Cue a cloud of “cool” hydrogen gas: at a temperature of around 10,000K, this cloud surrounds the black hole at a distance of a few light-years. Until now, it’s been unknown how this hydrogen reservoir interacts with the black hole’s hypothetical accretion disk and accretion flow, if at all.
ALMA is sensitive to the radio wave emissions that are generated by this cooler hydrogen gas, and has now been able to see how Sgr. A* is slurping matter from this vast hydrogen reservoir and pulling the cooler gas into its accretion disk—a feature that has, until now, been elusive to our telescopes. ALMA has basically used these faint radio emissions to act as a tracer as the cool gas mingles with the accretion disk, revealing its rotation and the location of the disk itself.
“We were the first to image this elusive disk and study its rotation,” said Elena Murchikova, a member in astrophysics at the Institute for Advanced Study in Princeton, New Jersey, in a statement. “We are also probing accretion onto the black hole. This is important because this is our closest supermassive black hole. Even so, we still have no good understanding of how its accretion works. We hope these new ALMA observations will help the black hole give up some of its secrets.” Murchikova is the lead author of the study published in Nature on June 6.
Located in the Chilean Atacama Desert, ALMA is comprised of 66 individual antennae that work as one interferometer to deliver observations of incredible precision. This is a bonus for these kinds of accretion studies, as ALMA has now probed right up to the edge of Sgr A*’s event horizon, only a hundredth of a light-year (or a few light-days) from the point of no return, providing incredible detail to the rotation of this cool disk of accreting matter. What’s more, the researchers estimate that ALMA is tracking only a minute quantity of cool gas, coming in at a total only a tenth of the mass of Jupiter.
A small quantity this may be (on galactic scales, at least), but it’s enough to allow the researchers to measure the Doppler shift of this dynamic flow, where some is blue-shifted (and therefore moving toward us) and some is red-shifted (as it moves away), allowing them to clock its orbital speed around the relentless maw of Sgr A*.
“We were able to shed new light on the accretion process around Sagittarius A*, which is a typical example of a class of black holes that have little to eat,” added Murchikova in a second statement. “The accretion behavior of these black holes is quite complex and, so far, not well understood.
“Our result is potentially important not only for our galaxy, but to any galaxy which has this type of underfed black hole in its heart. We hope that this cool disk will help us uncover more secrets of black holes and their behavior.”
The space telescope has refined the stellar flybys of the Voyager and Pioneer probes—how might it help us chart our way to the stars in the future?
When looking up on a starry night, it can be difficult to comprehend that those stars are not fixed in the sky. Sure, on timescales of a human lifetime, or even the entirety of human history, the stars don’t appear to move too much. But look over longer timescales—tens of thousands, to millions of years—and it becomes clear that the stars in the sky are in motion. This means the constellations we see today will be misshapen (or even non-existent!) in a few hundred thousand years’ time.
This poses an interesting question: If humanity were to send a spacecraft on an interstellar mission—an endeavor that could take thousands of years, depending on how ambitious the target—aiming it directly at a distant star would be a mistake. Depending on how far away that star is, by the time the spacecraft reaches its target, the star could have moved a few light-years away. This is why precision astrometry—the astronomical measurement of a star’s position, speed and direction of motion—will be needed to predict where a target star will be, and not where it currently is, when our future interstellar mission gets there.
To test this, we don’t need to wait until humanity has the means to build a starship, however. We have a bunch of interstellar probes that have already started their epic sojourns into the galaxy.
Earlier this year, NASA’s Voyager 2 spacecraft departed the Sun’s sphere of influence and became humanity’s second interstellar mission, six years after its twin, Voyager 1, made history to become the first human-made object to drift into the space between the stars. Both Voyagers are still transmitting telemetry to this day, over 40 years since their launch. Another two spacecraft, the older Pioneer 10 and 11 missions, are also on their way to interstellar space, but they stopped transmitting decades ago. A newcomer, NASA’s New Horizons mission, will also become an interstellar mission in the future, but it has yet to finish its Kuiper belt explorations and still has fuel to make course corrections, so predictions of its stellar encounters will remain unknown for some time.
Having explored the outer planets in the 1970’s and 80’s, the Voyagers and Pioneers barreled on, revealing stunning science from the outer solar system. In the case of Voyager 1 and 2, when each breached the heliopause (the invisible boundary that demarks the limit of the Sun’s magnetic bubble, between the heliosphere and interstellar medium), they gave us a profound opportunity to experience this distant alien environment, using their dwindling number of instruments to measure particle counts and magnetic orientation.
But where are our intrepid interstellar interlopers going now? With the help of precision astrometry of local stars observed by the European Space Agency’s Gaia space telescope, two researchers have taken a peek into the future, seeing which star systems the spacecraft will drift past in the next few hundred thousand to millions of years.
Previously, astronomers have been able to combine the spacecrafts’ trajectory with stellar data to see which stars they will fly past, but in the wake of the Gaia Data Release 2 (GDR2) last year, an unprecedented trove of information has been made available for millions of stars in the local galaxy, providing the most precise “road map” yet of those stars the Voyagers and Pioneers will encounter.
“[Gaia has measured] the positions and space velocities of nearby stars more precisely than before and so has more precisely characterized the encounters with stars we already knew about,” says astronomer Coryn Bailer-Jones, of the Max Planck Institute for Astronomy in Heidelberg, Germany.
Close Encounters of the Voyager Kind
Bailer-Jones and colleague Davide Farnocchia of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., published their study in Research Notes of the American Astronomical Society, adding another layer of understanding about where our spacecraft, and the stars they’ll encounter, are going. Although their work confirms previous estimates of some stellar close encounters, Bailer-Jones tells Astroengine.com that there have been some surprises in their calculations—including encounters that have not been identified before.
For example, the star Gliese 445 (in the constellation of Camelopardalis, close to Polaris) is often quoted as being the closest encounter for Voyager 1, in approximately 40,000 years. But with the help of Gaia, which is giving an extra layer of precision for stars further afield, the researchers found that the spacecraft will come much closer to another star, called TYC 3135-52-1, in 302,700 years.
“Voyager 1 will pass just 0.30 parsecs [nearly one light-year] from that star and thus may penetrate its Oort cloud, if it has one,” he says.
This is interesting. Keep in mind that the Voyager and Pioneer spacecraft include the famous Golden Records and plaques (respectively), revealing the location, form, and culture of a civilization living on a planet called “Earth.” For an alien intelligence to stumble across one of our long-dead spacecraft in the distant future, the closer the stellar encounter the better (after all, the likelihood of stumbling across a tiny spacecraft in the vast interstellar expanse would be infinitesimally small). Passing within one light-year of TYC 3135-52-1 is still quite distant (for instance, we currently have no way of detecting something as dinky as a Voyager-size probe zooming through the solar system’s Oort Cloud), but who knows what the hypothetical aliens in TYC 3135-52-1 are capable of detecting from their home world?
Another interesting thought is that these Gaia observations can help astronomers find stars that are currently very far away, but now we know their speed and direction of travel, some of those stars will be in our cosmic backyard in the distant future.
“What our study also found, for the first time, is some stars that are currently quite distant from the Sun will nonetheless come very close to one of the spacecraft within the next few million years,” says Bailer-Jones. “For example, the star Gaia DR2 2091429484365218432 is currently 159.5 parsecs [520 light-years] from the Sun (and thus from Voyager 1), but Voyager 1 will pass within 0.39 parsecs [1.3 light-years] of it in 3.4 million years from now.”
In some cases, given unlimited time, you may not have to go to a star, the star will come to you!
Our Interstellar Future?
While pinpointing the various stellar encounters for our first interstellar probes is interesting, the observations being made by Gaia will be important for when humanity develops the technology to make a dedicated effort to travel to the stars.
“It will be essential to have extremely precise astrometry of any target star,” explains Bailer-Jones. “We must also measure its velocity and its acceleration precisely, because these affect where the star will be when the spacecraft arrives.”
Although this scenario may seem a long way off, any precision astrometry we do now will build our knowledge of the local stellar population and boost the “legacy value” of Gaia’s observations, he adds.
“Once a target star has been selected, we would want to make a dedicated campaign to measure its position and velocity even more precisely, but to determine the accelerations we need data measured at many time points over long periods (at least tens of years), so Gaia data will continue to be invaluable in the future,” Bailer-Jones concludes.
“Even now, astrometry from the previous Hipparcos mission—or even from surveys from decades ago or photometric plates 100 years ago!—are important for this.”
Update (May 23): One of the reasons why I focused on the Voyager missions and not the Pioneers is because the latter stopped transmitting a long time ago. Another reason is because we already know Pioneer 10 doesn’t make it very far into interstellar space:
When Avery Broderick initially saw the first image from the Event Horizon Telescope (EHT), he thought it was too good to be true. After playing a critical role in the project since its inception in 2005, Broderick was staring at his ultimate quarry: a picture-perfect observation of a supermassive black hole in another galaxy. Not only was this first image sweet reward for the dedicated global effort to make the impossible possible, it was a beautiful confirmation of Broderick’s predictions and the 100-year-old theories of gravity they are based upon.
“It turns out our predictions were stunningly close; we were spot-on,” said Broderick. “I think this is a stunning confirmation that we are at least on the right track of understanding how these objects work.”
For Broderick, a professor at University of Waterloo and the Perimeter Institute for Theoretical Physics, and a key member of the international Event Horizon Telescope Collaboration, this wasn’t just an image that proved his theoretical models correct, it was the beginning of a historic journey into the unknown, with potentially revolutionary consequences that will reverberate through science and society as a whole.
Making the Impossible Possible
On April 10, the global collaboration showcased the first image of the supermassive black hole in the core of the massive elliptical galaxy M87. The image shows a ghostly bright crescent surrounding a dark disk, a feature that surrounds the most gravitationally extreme region known: a black hole’s event horizon. This first image isn’t only proof that humanity now has the ability to probe right up to the edge of an event horizon, it’s a promise that future observations will help us better understand how supermassive black holes work, how they drive the evolution of their galactic hosts and, possibly, reveal new physics by finally unmasking the true nature of gravity itself.
To Broderick, who has always been fascinated by the undiscovered, it’s mysteries like these that give him the passion to understand how the universe works – an adventure that is an important part of the human story.
“Black holes are the most extreme environments in the universe, so naturally I was hooked for as long as I can remember,” he said. “Nowhere in the universe is there a more perfect laboratory for pushing back the boundaries of our knowledge of gravity’s nature. That makes black holes irresistible.”
Few scientists would debate the reality of black holes, but the first image of M87’s supermassive black hole is definitive proof that these monsters, and their associated event horizons, exist. “These things are real, along with all the consequences for physics,” he said.
In the years preceding this announcement, Broderick and his EHT colleagues developed simulations that modeled what the Earth-spanning virtual telescope might see. And, on comparing his models with the first EHT image, Broderick was amazed.
“That first image was so good that I thought it was a test – it had to be a trial run,” said Broderick, “It’s a beautiful ring shape that’s exactly the right size. In fact, it looks very similar to the images (of theoretical models) we included in proposals for the EHT.”
The ring shape Broderick describes is the bright emissions from the hot gasses immediately surrounding the colossal maw of a supermassive black hole’s event horizon. Located inside the massive elliptical galaxy M87 in the constellation of Virgo, this gargantuan object has a mass of six-and-a-half-billion Suns and measures nearly half a light-day across. This may sound big, but because it’s located 55-million light-years away, it’s far too distant for any single telescope to photograph.
The EHT, however, is a network of many radio telescopes around the world, from the Atacama Desert to the South Pole. By working together – via a method known as very long-baseline interferometry – they create a virtual observatory as wide as our planet and, after two decades of development, the international collaboration has accomplished the impossible by resolving the event horizon around M87’s supermassive black hole.
“This is a project that has a wide breadth of collaboration, geographically – you can’t build an Earth-sized telescope without an Earth-sized collaboration! – but also in expertise, from the engineers who build these advanced telescopes, to the astronomers who work on the day-to-day and the theorists who inspire their observations,” said Broderick.
A Stunning Confirmation
The event horizon is a region surrounding a black hole where the known physics of our universe ends abruptly. Nothing, not even light, can escape a black hole’s incredible gravity, with the event horizon being the ultimate point of no return. What lies beyond the event horizon is open to debate, but one thing is for certain: if you fall inside, you’re not getting out.
Over a century ago, Albert Einstein formulated his theory of general relativity, a theoretical framework that underpins how our universe works, including how event horizons should look. Black holes are the embodiment of general relativity at its most extreme, and event horizons are a manifestation of where space-time itself caves in on itself.
“Event horizons are the end of the safe space of the universe,” said Broderick, “they should have ‘mind the gap’ or ‘mind the horizon’ signs around them!”
Physics has some key unresolved problems that may be answered by the EHT, one of which is the nature of gravity itself, added Broderick. Simply put, gravity doesn’t jibe with our current understanding of other fundamental forces and particles that underpin all matter in the universe. By stress-testing Einstein’s theories right at the edge of a black hole’s event horizon, the EHT will provide physicists with the ultimate laboratory in which to better understand gravity, the force that drives the formation of stars, planets, and the evolution of our universe.
Once we truly understand this fundamental force, the impact could be revolutionary, said Broderick. “Gravity is the key scientific problem facing physics today, and no one fully understands the ramifications of what understanding gravity fully are going to be.”
On an astronomical level, supermassive black holes are intrinsically linked with the evolution of the galaxies they inhabit, but how they form and evolve together is another outstanding mystery.
Supermassive black holes are also the purveyors of creation and doom – they have the power to kick-start star formation as well as preventing stars from forming at all – a dichotomy that astronomers hope to use the EHT to understand.
“These incredibly massive things lie at the centers of galaxies and rule their fates,” said Broderick. “Supermassive black holes are the engines behind active galactic nuclei and distant quasars, the most energetic objects known. Now we’re seeing what they look like, up close, for the first time.”
All galaxies are thought to contain a supermassive black hole, including our own galaxy, the Milky Way. Called Sagittarius A* (or Sgr A*), our supermassive black hole is 2,000 times less massive than the one in M87, but it’s 2,000 times closer – at a distance of 25,000 light-years. This means that the EHT can image both Sgr A* and M87 as they appear approximately the same size in the sky, a situation that is an incredible stroke of luck.
“If you had to choose two sources, these two would be it,” said Broderick. Whereas M87’s supermassive black hole is one of the biggest known and a “real mover and shaker,” Sgr A* is much less massive and considered to be an “everyman of black holes,” he said.
“We had to start somewhere. M87 represents the first end-to-end exercise of the entire EHT collaboration – from data taking to data interpretation,” said Broderick. “The next exercise will happen considerably faster. This is only the beginning.”
Voyage of Discovery
As the scientific benefits of observing supermassive black holes are becoming clear, Broderick pointed out that the impact on society could also be seismic.
“I would hope that an image like this will galvanize a sense of exploration; an exploration of the mind and that of the universe,” he said. “If we can excite people, inspire them to embark on a voyage of discovery in this new EHT era of observational black hole physics, I can only imagine that it will have profound consequences for humanity moving forward.
“I feel incredibly privileged to be a part of this story of exploration – the human story of understanding the universe we inhabit and using that understanding to improve our lives.”
The image is the result of a global collaboration and human ingenuity — a discovery that will change our perception of the universe forever
Lurking in the massive elliptical galaxy Messier 87 is a monster. It’s a supermassive black hole, 6.5 billion times the mass of our Sun, crammed inside an event horizon measuring half a light-day across. It’s very far away, over 50 million light-years, but, today, astronomers of the Event Horizon Telescope (EHT) have delivered on a promise that has been two decades in the making: They’ve recorded the first ever image of the bright ring of emissions immediately surrounding M87’s event horizon, the point at which our universe ends and only mystery lies beyond.
The magnitude of this achievement is historic. Not only does this single image prove that black holes actually exist, it is a stunning confirmation of the predictions of general relativity at its most extreme. If this theoretical framework acted somehow differently at the event horizon, the image wouldn’t look as it does. The reality is that general relativity has precisely predicted the size, shape and form of this distant object to an incredible degree of precision.
In the run-up to today’s announcement, I had the incredible fortune to write the University of Waterloo’s press release and feature about the EHT with Avery Broderick, a professor at Waterloo and the Perimeter Institute for Theoretical Physics, and a key member of the international EHT Collaboration. You can read the releases here:
I especially enjoyed discussing Avery’s personal excitement and passion for this project: “I would hope that an image like this will galvanize a sense of exploration; an exploration of the mind and that of the universe,” he said. “If we can excite people, inspire them to embark on a voyage of discovery in this new EHT era of observational black hole physics, I can only imagine that it will have profound consequences for humanity moving forward.”
Like the discovery of the Higgs boson and the detection of gravitational waves, the first image of a black hole will have as much of an impact on society as it will on science and, like Avery, I hope it inspires the next generation of scientists, driving our passion for exploration and understanding how our universe works.
Wow, what a morning.
Watch the NSF’s recording of today’s live feed here: