stellar physics – astroengine.com

Is Betelgeuse About to Blow? Maybe… Maybe Not

The famous supergiant on Orion’s shoulder has rapidly dimmed, stoking excitement that a supernova may be in the offing.

Artist’s impression of the tortured, bubbling photosphere of a dying Betelgeuse. [ESO/L. Calçada]

Do you hear that ticking? Doesn’t it sound like a stellar timer is counting down to the inevitable demise of a massive star? While the excitement may be the amplified construct of social media predictions of the death of Betelgeuse, our stellar neighbor really is close to going supernova.

“Close”, however, is relative. It could be as “human close” as blowing up any minute now… to “galactic close” as blowing up in a hundred thousand years, maybe more.

So, what’s all the fuss about? In a nutshell, the brightest star in the famous constellation of Orion is bright no more. In the past few weeks, Betelgeuse has dimmed noticeably, stoking predictions that it could be about to spectacularly erupt at any time, becoming as bright as a full Moon and casting its own shadows at night.

While this may sound ominous, a Betelgeuse supernova poses no threat to life on Earth. It’s located a safe 600 light-years away, so if it did explode, we’d be treated to a historic cosmic firework display and not doomsday. Any energetic particles spewing from the explosion may reach the solar system in 100,000 years, but would have a minimal impact; the heliosphere (our Sun’s extended magnetic “bubble” that encompasses all the planets) would be more than powerful enough to deflect the tenuous gases.

The constellation of Orion, with the ruddy Betelgeuse in the upper left-hand corner on Orion’s “shoulder.” [Photo by **Frank Cone** from **Pexels**]

There has always been excitement over Betelgeuse and its explosive potential. It’s a massive star, with a mass 12-times that of our Sun, which has reached the end of its life. But with a lifespan of only eight million years or so, it may sound odd that it’s dying of old age. As a comparison, our Sun—an “average” yellow dwarf star—sounds geriatric in comparison; it’s approximately five billion years old. But the strange physics of stellar evolution dictates that the more massive the star, the shorter its lifespan. Betelgeuse is on borrowed time, whereas our Sun is only middle-aged. In other words, Betelgeuse has lived fast and it will die young.

As a star that’s about to die, Betelgeuse is experiencing the final throes of violent processes that signify the conclusion of stellar evolution—a phase that sees a massive star puff up into a red supergiant. In the case of Betelgeuse, while it is 12-times more massive than our Sun, it has expanded into a grotesque, bubbling mess of superheated plasma, puffed up to nearly 1,000-times wider than our Sun. If Betelgeuse were transplanted into the middle of our solar system, it would swallow all the planets out to Saturn. Yes, even Jupiter would be ingested.

A precision observation of Betelgeuse’s asymmetric photosphere, highlighting bright spots and a non-spherical shape, as captured by the Atacama Large Millimeter/submillimeter Array (ALMA).

After guzzling all of its hydrogen fuel long ago, it’s now fusing heavier elements inside its tortured interior to the point where iron is being created. For any massive star, the fusion of iron is the death knell; energy is being absorbed, and soon, its immense gravity will cause the whole mess to collapse, generating an almighty shockwave that will, ultimately, rip Betelgeuse apart as a supernova.

As reported by astronomers before Christmas, the observed dimming could be interpreted as a precursor to the anticipated supernova, and for good reason. But Betelgeuse is known to regularly vary in brightness, so astronomers suspect that, while this is an unprecedented dimming event, the famous star will soon return to its “regular” brightness once more, reclaiming its rank as ninth brightest star in the sky.

In short, don’t place any serious money on Betelgeuse exploding soon. While there is a tiny chance that it might have already exploded, the light from the supernova currently galloping across the 600 light-year interstellar divide between us and Betelgeuse, it’s way more likely that it’s just Betelgeuse being Betelgeuse and keeping variable star astronomers on their toes.

That’s not to say the dimming event isn’t exciting, on the contrary. Seeing a prominent star in the night sky fade with your own eyes is something to behold, so when you get clear skies, look for Orion and ponder The Hunter’s missing shoulder.

Catching a Star’s Helium Flash

Old stellar flashers will be caught in the act in the not-so-distant future, whether they like it or not.

While we have a pretty good idea about how stars like our Sun work, observing all the details that unfold over millions to billions of years of stellar evolution can be difficult, especially if the phenomena occur over short timescales. Take, for example, a particularly explosive and relatively short-lived period our Sun is expected to experience in roughly five billion years.

This event is predicted to happen after our nearest star has burned up all of its hydrogen fuel and starts to burn helium. This is the beginning of the end; the Sun will swell into a vast red giant, ejecting its upper layers of plasma into space via violent solar winds, brightening 1,000 times than it is today. Needless to say, this will be a terribly dramatic time for our solar system (and a definitive apocalypse for anything that remains of our planet’s biosphere), but it will be on the verge of something even more dramatic: a helium flash.

As the solar core starts using helium as fuel, the fusion process will generate carbon and as this begins, a powerful eruption of energy will detonate, as detailed by a UC Santa Barbara statement:

A star like the sun is powered by fusing hydrogen into helium at temperatures around 15 million K. Helium, however, requires a much higher temperature than hydrogen, around 100 million K, to begin fusing into carbon, so it simply accumulates in the core while a shell of hydrogen continues to burn around it. All the while, the star expands to a size comparable to the Earth’s orbit. Eventually, the star’s core reaches the perfect conditions, triggering a violent ignition of the helium: the helium core flash. The core undergoes several flashes over the next 2 million years, and then settles into a more static state where it proceeds to burn all of the helium in the core to carbon and oxygen over the course of around 100 million years.

While the helium flashes of old Sun-like stars have been predicted for 50 years, we have yet to actually observe any kicking off in our galaxy, which isn’t so surprising considering it’s only comparatively recently that we’ve developed the techniques that are capable of precisely measuring the brightness fluctuations of distant stars. This might be about to change, according to a new study published in Nature Astronomy Letters.

“The availability of very sensitive measurements from space has made it possible to observe subtle oscillations in the brightness of a very large number of stars,” said coauthor Jørgen Christensen-Dalsgaard, of the UC Santa Barbara’s Kavli Institute for Theoretical Physics (KITP).

Christensen-Dalsgaard is referring to the growing number of space-based observatories, primed to survey the sky for transiting exoplanets—such as Kepler, CoRoT and TESS—that have extremely sensitive photonics that can detect the slightest changes in stellar brightness. And by virtue of these missions’ wide field of view, taking in the light from many stars at once, the helium flashes and resulting brightness oscillations across the stars’ surfaces could be detected in the near future.

It’s thought that the flash itself should last for no more than two million years, which may sound like a long time to we puny humans, but over cosmic timescales, that’s literally a flash—we need some serious luck to detect them. But with more observatories, longer observation periods, and wider fields of view, luck may be just around the corner.

Heavy Stellar Traffic Sends Dangerous Comets Our Way

New image of comet ISON — Comet C/2012 S1 (ISON) as imaged by TRAPPIST–South national telescope at ESO’s La Silla Observatory in 2013 (TRAPPIST/E. Jehin/ESO)

Sixty-six million years ago Earth underwent a cataclysmic change. Back then, our planet was dominated by dinosaurs, but a mass extinction event hastened the demise of these huge reptiles and paved the way for the mammalian takeover. Though there is some debate as to whether the extinction of the dinosaurs was triggered by an isolated disaster or a series of disasters, one event is clear — Earth was hit by a massive comet or asteroid and its impact had global ramifications.

The leading theory is that a massive comet slammed into our planet, creating the vast Chicxulub Crater buried under the Yucatán Peninsula in Mexico, enshrouding the atmosphere in fine debris, blotting out the sun for years.

Although there is strong evidence of comet impacts on Earth, these deep space vagabonds are notoriously hard to track, let alone predict when or how often they may appear. All we know is that they are out there, there are more than we thought, they are known to hit planets in the solar system and they can wreak damage of apocalyptic proportions.

Now, using fresh observations from the European Space Agency’s Gaia mission, astronomer Coryn Bailer-Jones, who works at the Max Planck Institute for Astronomy in Munich, Germany, has added an interesting component to our understanding of cometary behavior.

Stellar Traffic

Long-period comets are the most mysterious — and troubling — class of comet. They will often appear from nowhere, after falling from their distant gravitational perches, zoom through the inner solar system and disappear once more — often to be never seen again. Or they hit something on their way through. These icy bodies are the pristine left-overs of our solar system’s formation five billion years ago, hurled far beyond the orbits of the planets and into a region called the Oort Cloud.

In the Oort Cloud these ancient masses have remained in relative calm far from the gravitational instabilities close to the sun. But over the eons, countless close approaches by other stars in our galactic neighborhood have occurred, causing very slight gravitational nudges to the Oort Cloud. Astronomers believe that such stellar encounters are responsible for knocking comets from this region, sending them on a roller-coaster ride to the inner solar system.

The Gaia mission is a space telescope tasked with precisely mapping the distribution and motion of stars in our galaxy, so Bailer-Jones has investigated the rate of stellar encounters with our solar system. Using information in Gaia’s first data release (DR1), Bailer-Jones has published the first systematic estimate of stellar encounters — in other words, he’s estimated the flow of stellar traffic in the solar system’s neighborhood. And the traffic was found to be surprisingly heavy.

In his study, to be published in the journal Astronomy & Astrophysics, Bailer-Jones estimates that, on average, between 490 and 600 stars will come within 16.3 light-years (5 parsecs) of our sun and 19-24 of them will come within 3.26 light-years (1 parsec) every million years.

According to a press release, all of these stars will have some gravitational effect on the solar system’s Oort Cloud, though the closest encounters will have a greater influence.

This first Gaia data release is valid for five million years into the past and into the future, but astronomers hope the next data release (DR2) will be able to estimate stellar traffic up to 25 million years into the past and future. To begin studying the stellar traffic that may have been responsible for destabilizing the dinosaur-killing comet that hit Earth 66 million years ago will require a better understanding of the mass distribution of our galaxy (and how it influences the motion of stars) — a long-term goal of the Gaia project.

An Early Warning?

Spinning this idea into the future, could this project be used to act as an early warning system? Or could it be used to predict when and where a long-period comet may appear in the sky?

In short: “No,” Bailer-Jones told Astroengine via email. “Some close stellar encounters will for sure shake up the Oort cloud and fling comets into the inner solar system, but which comets on which orbits get flung in we cannot observe.”

He argues that the probability of comets being gravitationally nudged can be modeled statistically, but this would require a lot of assumptions to be made about the Oort Cloud, a region of space that we know very little about.

Also, the Oort Cloud is located well beyond the sun’s heliosphere and is thought to be between 50,000 and 200,000 AU (astronomical units, where 1 AU is the average distance between the sun and the Earth) away, so it would take a long time for comets to travel from this region, creating a long lag-time between stellar close approach and the comet making an appearance.

“Typically it takes a few million years for a comet to reach the inner solar system,” he added, also pointing out that other factors can complicate calculations, such as Jupiter’s enormous gravity that can deflect the passage of comets, or even fling them back out of the solar system again.

This is a fascinating study that goes to show that gravitational perturbations in the Oort Cloud are far from being rare events. A surprisingly strong flow of stellar traffic will constantly rattle otherwise inert comets, but how many are dislodged and sent on the long journey to the solar system’s core remains a matter for statistics and probability.

Battlestar Galactica’s “Twelve Colonies of Kobol” Star System Found?

An image at radio wavelengths of a young stellar quadruplet. Credit: CfA/Nature/Pineda

825 light-years away, in the constellation of Perseus, hides one protostar and three previously unseen gas concentrations that are undergoing gravitational collapse — basically embryos of soon-to-be baby stars. Found through the analysis of data from radio telescopes by astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA), this tiny cluster of baby stars occupy a small volume only 10,000 AU across — meaning that they’d all easily fit within the confines of the boundaries of our solar system (yes, the Oort Cloud is the solar system’s outermost boundary).

This is exciting for a couple of reasons. Firstly, this little ‘stellar womb’ has given astronomers an opportunity to study the genesis of a multi-star system. Indeed, most stars in our galaxy belong to multi-star systems, whether that be binary or greater, and astronomers are currently trying to figure out whether they were born this way or whether, over time, stars jostled around and eventually became gravitationally bound. After analysis of the velocities of the protostar and stellar embryos, it appears that the masses are gravitationally interacting. In other words, it has the potential to mature into a quadruple star system in around 40,000 years, a minute amount of time in cosmic timescales. Although it is likely that the system will become unstable, possibly ejecting one or two of the stars in the process, it does provide observational evidence that multi-star systems can be born in a gravitational embrace.

A map of the Twelve Colonies via io9.com

But as I have a habit of linking astrophysical studies with science fiction imaginings, when I first saw this research, I immediately thought of the awesome re-imagined series’ Battlestar Galactica and Caprica.

Battlestar Galactica is set in the years following the Cylon attack on the Twelve Colonies of Kobol, which almost wiped out humanity in this far-flung part of the galaxy. The remaining survivors, headed by William Adama (Edward James Olmos), take to the stars in a fleet of ragtag spaceships in search of the fabled Earth. One of my favorite scifi storylines and favorite scfi TV shows. But I digress.

The Twelve Colonies consist of four stars — Helios Alpha, Helios Beta, Helios Delta and Helios Gamma — each with their own systems of planets, 12 in total, including capital world Caprica.

So that poses a question: Just because Battlestar Galactica imagines a quadruple star system (well, two binary systems in a mutual orbit), is it possible to have such a stable system of planets evolve in a multi-star system? Or are the gravitational interactions too complex for anything to coalesce and slot into stable orbits? Well, by understanding how multi-star systems evolve by finding examples like this embedded inside star forming molecular clouds, we may start to appreciate how common and how stable they are and whether accompanying planetary systems are a reality or something that will forever be confined to the Twelve Colonies.