Will the EHT’s First Black Hole Image Look Like Interstellar’s “Gargantua”?

Not quite.

The supermassive black hole “Gargantua” from the movie “Interstellar.” [Paramount Pictures]

UPDATE: The EHT’s first image has been released! See: This Is the First Image of a Black Hole

Tomorrow, on April 10, the Event Horizon Telescope (EHT) will make an international announcement about a “groundbreaking result” from the global collaboration. Further details as to what this result actually is are under wraps, but as the EHT’s mission is to image a supermassive black hole for the first time, the expectation is that it will be a historic day for humanity. We may actually see what a black hole — more precisely, a black hole’s event horizon — really looks like.

But we already know what a black hole looks like, right? There have been countless science fiction imaginings of black holes over the years and, most recently, the Matthew McConaughey movie “Interstellar” depicted what is touted as the most scientifically-accurate sci-fi black hole ever.

Diving into a black hole has never been so much fun [Paramount Pictures]

Interstellar’s black hole, called “Gargantua,” is a sight to behold and many physicists and CGI experts went out of their way to base that thing on the physics that is predicted to drive these monsters. Physics heavyweight Kip Thorne even advised on how this rotating black hole — a supermassive one at that — should look and behave, based on earlier work by Jean-Pierre Luminet (ScienceAlert has a great article about this).

Back to reality, the EHT may well be presenting its own “Gargantua moment” tomorrow when the first results are presented. The EHT is a global network of radio telescopes all dedicated to probing the final frontier of general relativity. Black holes are the most extreme gravitational objects in the universe and the supermassive monsters that lurk in the cores of most galaxies are true behemoths.

The EHT currently has two targets it hopes to image, the supermassive black hole in the core of our galaxy, the Milky Way, and one inside the massive elliptical galaxy, M87. With a mass of four million Suns, our galaxy’s supermassive black hole is called Sagittarius A* (Sgr A* for short) and is located approximately 25,000 light-years away. But M87’s monster dwarfs our comparatively diminutive specimen — it’s a super-heavyweight among supermassive black holes, with a mass of a whopping 6.5 billion Suns.

In a wonderful stroke of cosmic luck, although M87 is 50 million light-years away, some 2,000 times further away than Sgr A*, it’s also approximately 2,000 times more massive. This means that both Sgr A* and M87 will appear approximately the same size in the sky to the EHT. They are also two wonderful targets to study, as both are very different in nature.

Now, back to Gargantua. As this CGI beauty is based on real physics theory, and assuming the first EHT image doesn’t throw the fidelity of general relativity into doubt, both Gargantua and the two EHT targets should, basically, look the same. Sure, there’s going to be differences based on mass, jets of material, size of accretion disks and other details, but will the EHT first image bear any resemblance to the Interstellar rendering?

Short answer: no, it should look something like this:

Screen capture from Avery Broderick’s 2015 Convergence presentation on the theoretical efforts behind the EHT. Broderick is a professor at the Perimeter Institute and University of Waterloo, and a member of the EHT collaboration. More on this here.

Long answer: It’s all about wavelength. Over to gravitational wave astrophysicist Dr. Chiara Mingarelli, of the Flatiron Center for Computational Astrophysics (CCA), who’s tweet inspired this article:

Gargantua was created with human vision in mind. Our eyes are sensitive to visual wavelengths, from 380 nanometers (violet) to 740 nanometers (red), and movies are very much based on what humans can see (I hear infrared movies are rubbish). But the EHT cares little for nanometer wavelengths — the EHT is all about seeing the universe in millimeter wavelengths, which means it can see things our eyes can’t see. It is a network of radio telescopes all working together as one planet-wide virtual telescope via a clever method known as very long baseline interferometry. By viewing a black hole target at these wavelengths, astronomers have the ability to see straight through the accretion disk, dusty torus (if it has one), jets of material and other nonsense floating around the black hole.

Here’s a few frames from the simulation Dr. Mingarelli is referring to above, wavelength increasing from nanometers to millimeters, left to right:

Frames from the black hole simulation. As the wavelength increases from left to right, features such as the black hole’s accretion disk becomes transparent, allowing the EHT to see emissions from just outside the edge of the event horizon — seen here as a small silhouetted disk (far right). [Credit: Chi-Kwan Chan]

The EHT can see right up to the innermost limit, just before nothing, not even light, can escape the gravitational grasp of the event horizon. Any hot plasma or dust that would otherwise obscure our view of the horizon are transparent at wavelengths more than one millimeter, so we can see the radiation emitted by the hot, turbulent material that is being tortured by the extreme environment right at the horizon.

Gargantua is a glorious rendering of what a supermassive black hole might look like if we could take a trip with Matthew McConaughey and co. (give or take some CGI sparkle for dramatic effect). What the EHT sees is the shadow, or the silhouette, of a black hole’s event horizon — that will likely be either perfectly circular or slightly oblate, if general relativity holds. That’s not to say that Gargantua doesn’t look like Sgr. A* or M87 in visible wavelengths as Hollywood intended, it’s just that the EHT will lack most of Gargantua’s CGI.

So, I’ll be waking up far earlier tomorrow to watch the EHT announcement and keeping my fingers crossed that we’ll finally get to see what an event horizon really looks like.

Voyager 2 Has Left the (Interplanetary) Building

The NASA probe was launched in 1977 and has now joined its twin, Voyager 1, to begin a new chapter of interstellar discovery

Both Voyager 1 and 2 are sampling particles from the interstellar medium, becoming humanity’s furthest-flung missions into deep space [NASA/JPL-Caltech]

Carolyn Porco, planetary scientist and lead of the NASA Cassini mission imaging team, probably said it best:

Voyager 1 made us an interstellar species; 6 yrs later, Voyager 2 makes it look easy. While these are historic, soul-stirring achievements, I am most happy right now that Ed Stone, the best Project Scientist who ever lived, lived to see this moment. 

via Twitter

It can be easy to lump today’s announcement about Voyager 2 entering interstellar space as “simply” another magnificent science achievement for NASA — but that would be too narrow; the Voyager spacecraft have become so much more. They represent humanity at our best; our will to explore, our need to push boundaries, our excitement for expanding the human experience far beyond terrestrial shores. They also act as a means to understand the sheer scale of our solar system. And what better way to measure that scale than with a human life. 

Ed Stone started working on the Voyager Program in 1972 as a project scientist. Now, at 82 years old, he’s still working on the Voyagers nearly half a century later as they continue to send back data from the frontier beyond our solar system. When we start measuring space missions in half-centuries, or missions that have lasted entire careers, it becomes clear how far we’ve come. Not only does NASA build really tough space robots that surpass expectations routinely, returning new discoveries and revelations about the universe that surrounds us, the Voyagers have become a monument to the essence of being human, something with which Stone would probably agree.

Although most of the instruments aboard the Voyagers are no longer functional, both missions are still returning data from the shores of the interstellar ocean and, on Nov. 5, mission controllers noticed that one of Voyager 2’s instruments, the Plasma Science Experiment (PSE), had detected a rapid change in its surrounding environment. Used to being immersed the comparatively warm and tenuous solar wind flowing past it, its plasma measurements detected a change. The spacecraft had passed into a region of space where the plasma was now denser and cooler. Three other particle experiments also detected a dramatic change; solar wind particle counts were down, but cosmic ray counts precipitously increased. Voyager 1’s PSE failed in 1980, so couldn’t measure this boundary when it entered interstellar space in 2012, so Voyager 2 is adding more detail about what we can expect happens when a spacecraft travels from the heliosphere, through the heliopause and into interstellar space. 

[NASA/JPL-Caltech]

“There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Stone in a NASA statement.

The heliosphere can be imagined as a vast magnetized bubble that is generated by the Sun. This bubble is inflated by the solar wind, a persistent stream of solar particles that ebb and flow with the Sun’s 11-year cycle. When the Sun is at its most active, the bubble expands; at its least active, it contracts. This dynamic solar sphere of influence affects the flux of high-energy cosmic rays entering the inner solar system, but the physics at this enigmatic boundary is poorly understood. With the help of the Voyagers, however, we’re getting an in-situ feel for the plasma environment at the boundary of where the Sun’s magnetism hits the interstellar medium.

To achieve this, however, we had to rely on two spacecraft that were launched before I was born, in 1977. Voyager 2 is now 11 billion miles away (Voyager 1 is further away, at nearly 14 billion miles) and it took the probe 41 years just to reach our interstellar doorstep. Neither Voyagers have “left” the solar system, not by a long shot. The gravitational boundary of the solar system is thought to lie some 100,000 AU (astronomical units, where one AU is the average distance from the Earth to the Sun), the outermost limit to the Oort Cloud — a region surrounding the solar system that contains countless billions of icy objects, some of which become the long-period comets that intermittently careen through the inner solar system. Voyager 2 is barely 120 AU from Earth, so as you can see, it has a long way to go (probably another 30,000 years) before it really leaves the solar system — despite what the BBC tells us.

So, tonight, as we ponder our existence on this tiny pale blue dot, look up and think of the two space robot pioneers that are still returning valuable data despite being in deep space for over four decades. I hope their legacy lives on well beyond the life of their radioactive generators, and that the next interstellar spacecraft (no pressure, New Horizons) lives as long, if not longer, than the Voyagers.

Read more about today’s news in my article for HowStuffWorks.com.

  

Hitching a Ride on an ‘Evolving Asteroid’ to Travel to the Stars

evolvingaste
The interstellar asteroid spaceship concept that would contain all the resources required to maintain a generations of star travelers (Nils Faber & Angelo Vermeulen)

When ʻOumuamua visited our solar system last year, the world’s collective interest (and imagination) was firing on all cylinders. Despite astronomers’ insistence that asteroids from other star systems likely zip through the solar system all the time (and the reason why we spotted this one is because our survey telescopes are getting better), there was that nagging sci-fi possibility that ʻOumuamua wasn’t a natural event; perhaps it was an interstellar spaceship piloted by (or at least once piloted by) some kind of extraterrestrial — “Rendezvous With Rama“-esque — intelligence. Alas, any evidence for this possibility has not been forthcoming despite the multifaceted observation campaigns that followed the interstellar vagabond’s dazzling discovery.

Still, I ponder that interstellar visitor. It’s not that I think it’s piloted by aliens, though that would be awesome, I’m more interested in the possibilities such objects could provide humanity in the future. But let’s put ʻOumuamua to one side for now and discuss a pretty nifty project that’s currently in the works and how I think it could make use of asteroids from other stars.

Asteroid Starships Ahoy!

As recently announced by the European Space Agency, researchers at Delft University of Technology, Netherlands, are designing a starship. But this isn’t your run-of-the-mill solar sail or “warpship.” The TU Delft Starship Team, or DSTART, aims to bring together many science disciplines to begin the ground-work for constructing an interstellar vehicle hollowed out of an asteroid.

Obviously, this is a long-term goal; humanity is currently having a hard enough time becoming a multiplanetary species, let alone a multistellar species. But from projects like these, new technologies may be developed to solve big problems and those technologies may have novel applications for society today. Central to ESA’s role in the project is an exciting regenerative life-support technology that is inspired by nature, a technology that could reap huge benefits not only for our future hypothetical interstellar space fliers.

Called the MELiSSA (Micro-Ecological Life Support System Alternative) program, scientists are developing a system that mimics aquatic ecosystems on Earth. A MELiSSA pilot plant in Barcelona is capable of keeping rat “crews” alive for months at a time inside an airtight habitat. Inside the habitat is a multi-compartment loop with a “bioreactor” at its core, which consists of algae that produces oxygen (useful for keeping the rats breathing) while scrubbing the air of carbon dioxide (which the rats exhale). The bioreactor was recently tested aboard the International Space Station, demonstrating that the system could be applied to a microgravity environment.

Disclaimer: Space Is Really Big

Assuming that humanity isn’t going to discover faster-than-light (FTL) travel any time soon, we’re pretty much stuck with very pedestrian sub-light-speed travel times to the nearest stars. Even if we assume some sensible iterative developments in propulsion technologies, the most optimistic projections in travel time to the stars is many decades to several centuries. While this is a drag for our biological selves, other research groups have shown that robotic (un-crewed) missions could be done now — after all, Voyager 1 is currently chalking up some mileage in interstellar space and that spacecraft was launched in the 1970’s! But here’s the kicker: Voyager 1 is slow (even if it’s the fastest and only interstellar vehicle humanity has built to date). If Voyager 1 was aimed at our closest star Proxima Centauri (which it’s not), it would take tens of thousands of years to get there.

But say if we could send a faster probe into interstellar space? Projects like Icarus Interstellar and Breakthrough Starshot are approaching this challenge with different solutions, using technology we have today (or technologies that will likely be available pretty soon) to get that travel time down to less than one hundred years.

One… hundred… years.

Sending robots to other stars is hard and it would take generations of scientists to see an interstellar mission through from launch to arrival — which is an interesting situation to ponder. But add human travelers to the mix? The problems just multiplied.

The idea of “worldships” (or generation ships) have been around for many years; basically vast self-sustaining spaceships that allow their passengers to live out their lives and pass on their knowledge (and mission) to the next generation. These ships would have to be massive and contain everything that each generation needs. It’s hard to comprehend what that starship would look like, though DSTART’s concept of hollowing out an asteroid to convert it into an interstellar vehicle doesn’t sound so outlandish. To hollow out an asteroid and bootstrap a self-sustaining society inside, however, is a headache. Granted, DSTART isn’t saying that they are actually going to build this thing (their project website even states: “DSTART is not developing hardware, nor is it building an actual spacecraft”), but they do assume some magic is going to have to happen before it’s even a remote possibility — such as transformative developments in nanotechnology, for example. The life-support system, however, would need to be inspired by nature, so ESA and DSTART scientists are going to continue to help develop this technology for self-sustaining, long-duration missions, though not necessarily for a massive interstellar spaceship.

Hyperbolic Space Rocks, Batman!

Though interesting, my reservation about the whole thing is simple: even if we did build an asteroid spaceship, how the heck would we accelerate the thing? This asteroid would have to be big and probably picked out of the asteroid belt. The energy required to move it would be extreme; to propel it clear of the sun’s gravity (potentially via a series of gravitational assists of other planets) could rip it apart.

So, back to ʻOumuamua.

The reason why astronomers knew ʻOumuamua wasn’t from ’round these parts was that it was moving really, really fast and on a hyperbolic trajectory. It basically barreled into our inner star system, swung off our sun’s gravitational field and slingshotted itself back toward the interstellar abyss. So, could these interstellar asteroids, which astronomers estimate are not uncommon occurrences, be used in the future as vehicles to escape our sun’s gravitational domain?

Assuming a little more science fiction magic, we could have extremely advanced survey telescopes tasked with finding and characterizing hyperbolic asteroids that could spot them coming with years of notice. Then, we could send our wannabe interstellar explorers via rendezvous spacecraft capable of accelerating to great speeds to these asteroids with all the technology they’d need to land on and convert the asteroid into an interstellar spaceship. The momentum that these asteroids would have, because they’re not gravitationally bound to the sun, could be used as the oomph to achieve escape velocity and, once setting up home on the rock, propulsion equipment would be constructed to further accelerate and, perhaps, steer it to a distant target.

If anything, it’s a fun idea for a sci-fi story.

I get really excited about projects like DSTART; they push the limits of human ingenuity and force us to find answers to seemingly insurmountable challenges. Inevitably, these answers can fuel new ideas and inspire younger generations to be bolder and braver. And when these projects start partnering with space agencies to develop existing tech, who knows where they will lead.

The Solar System Just Had an Interstellar Visitor. Now It’s Gone

Comet-PanSTARRS-1
Hello, goodbye interstellar comet. The hyperbolic orbit of Comet C/2017 C1 as plotted by JPL’s Small-Body Database Browser (NASA/JPL-Caltech)

Update: At original time of writing, C/2017 U1 was assumed to be a comet. But Followup observations by the Very Large Telescope in Chile on Oct. 25 found no trace of cometary activity. The object’s name has now been officially changed to A/2017 U1 as it is more likely an interstellar asteroid, not a comet.

Astronomers using the PanSTARRS 1 telescope in Maui may have discovered an alien comet.

Comets and asteroids usually originate from the outermost reaches of the solar system — they’re the ancient rocky, icy debris left over from the formation of the planets 4.6 billion years ago.

However, astronomers have long speculated that comets and asteroids originating from other stars might escape their stars, traverse interstellar distances and occasionally pay our solar system a visit. And looking at C/2017 U1’s extreme hyperbolic trajectory, it looks very likely it’s not from around these parts.

“If further observations confirm the unusual nature of this orbit this object may be the first clear case of an interstellar comet,” said Gareth Williams, associate director of the International Astronomical Union’s Minor Planet Center (MPC). A preliminary study of C/2017 U1 was published earlier today. (Since this statement, followup observations have indicated that the object might be an asteroid and not a comet.)

According to Sky & Telescope, the object entered the solar system at the extreme speed of 16 miles (26 kilometers) per second, meaning that it is capable of traveling a distance of 850 light-years over 10 million years, a comparatively short period in cosmic timescales.

Spotted on Oct. 18 as a very dim 20th magnitude object, astronomers calculated its trajectory and realized that it was departing the solar system after surviving a close encounter with the sun on Sept. 9, coming within 23.4 million miles (0.25 AU). Comets would vaporize at that distance from the sun, but as C/2017 U1’s speed is so extreme, it didn’t have time to heat up.

“It went past the sun really fast and may not have had time to heat up enough to break apart,” said dynamicist Bill Gray. Gray estimates that the comet is approximately 160 meters wide with a surface reflectivity of 10 percent.

But probably the coolest factor about this discovery is the possible origin of C/2017 U1. After calculating the direction at which the comet entered the solar system, it appears to have come from the constellation of Lyra and not so far from the star Vega. For science fiction fans this holds special meaning — that’s the star system where the SETI transmission originated in the Jodie Foster movie Contact.

For more on this neat discovery, check out the Sky & Telescope article.