A Black Hole in Our Own Backyard

Michio Kaku: We now have bagged some of the biggest black holes ever recorded in the history of science that have gobbled up over 20 billion stars.  What a feast of astronomical activity.  These gigantic black holes lurk at the center of galaxies.  We have one right in the center of the Milky Way Galaxy, and in fact, if you want to see a black hole tonight, go outside, look in the direction of Sagittarius--that’s where we have the center of the galaxy and a black hole weighing perhaps two to four million times the mass of the sun lurking right at the center of our own backyard.  

Now, to be real, you’re not going to see much tonight if you look in the direction of Sagittarius because of clouds and also galactic dust clouds.  The galaxy is quite dusty.  That’s what we’re made out of in fact.  We’re made out of galactic dust.  And if you look at the center of the Milky Way Galaxy by rights you should see a fireball, a fireball that outshines the moon.  Every night there should be this gigantic fireball coming out representing the center of our galaxy, but dust clouds obscure it, so you don’t really see much of anything at all.  But lurking in that direction is the black hole at the center of our galaxy.  

Our black hole is actually rather small and rather tame, but these black holes discovered just a few weeks ago are so massive that we believe that they are actually remnants of quasars.  Quasars are baby galaxies that were born near the beginning of the universe itself that are raging black holes in space.  They are so bright you can easily pick them out in photographs on the planet earth and they date all the way back to almost the Big Bang itself.  

But what happened to the quasars?  We don’t see quasars in our galactic vicinity anymore.  So they must have become quiet.  So some people believe that these giant black holes that we just discovered are in fact baby quasars that simply got old and matured, and now we see them as gigantic black holes lurking in space.  

Well, some people say let’s go in the opposite direction and find mini black holes.  Are they dangerous?  Well, realize that we orbit, we orbit around the black hole at the center of the Milky Way Galaxy.  That’s why we’re here today to talk about this on the Internet.  We’re not swallowed up by a black hole because we orbit around them.  However, are there wandering black holes?  And the answer is yes.  In fact, we’ve been able to track wandering black holes as they wander through the galaxy.  One day, one of them may catch up with us and eat us for breakfast and it wouldn’t even burp in the process.  

Now, a black hole is black.  It’s invisible, so how the hell do we know that there is a wandering black hole in our vicinity?  The answer is quite easy.  It was found by accident by taking a picture of the night sky, and taking the same picture at a different time, you see a distortion, a distortion of light and then like time lapse if you put these photographs together you see that the distortion goes in a straight line.  And then you say “Aha, that’s the black hole.”  Even though it’s invisible it distorts light.  For example, many people wear glasses.  There is glass inside your glasses, but how do you know that?  How do you know that there is glass inside your glasses when glass is invisible?  Well it’s obvious.  Glass distorts light.  That’s how you know that something that is invisible is actually there, and the same thing with black holes.  They’re invisible, but they distort star light as they move.  And these are mini black holes.  They weigh a few times more than our sun but they’re massive enough to disrupt the entire solar system if one day one creeps up behind us.

So one day if a wandering black hole snuck up behind us, how would we know?  First of all, Pluto and Neptune would begin to perturb.  Some of them would be, in fact, flung into outer space.  As the black hole got closer and closer to Planet Earth we would see more and more disruptions in the solar system as more planets got flung into outer space.  And, in fact, as it whizzed by the earth it could even gobble up the earth, in fact, eat up the sun and hardly even notice.  And so the appetite of a black hole would be enormous, and it’s something that at some point in the future we may encounter, that is, a wandering black hole in our own backyard.  

Directed / Produced by
Jonathan Fowler & Elizabeth Rodd

 

A wandering black hole may catch up with us one day and eat us for breakfast and it wouldn’t even burp in the process.

Photo: Luisa Conlon , Lacy Roberts and Hanna Miller / Global Oneness Project
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It seems that pretty much every galaxy we see is spinning around a supermassive black hole. When we say "supermassive," we mean BIG: Each is about 100,000 to tens of billions times the mass of our Sun. Serving as the loci around which our galaxies twirl, they're clearly important to maintaining the universal structures we see. It would be nice to know how they form. We have a pretty good idea how normally-huge-but-not-massive black holes form, but as for the supermassive larger versions, not so much. It's a supermassive missing piece of the universe puzzle.

Now, in research published in Monthly Notices of the Astronomical Society, astrophysicists at Tohoku University in Japan reveal that they may have solved the riddle, supported by new computer simulations that show how supermassive black holes come to be.

The direct collapse theories

Glowing gas and dark dust within the Large Magellanic Cloud

Image source: ESA/Hubble and NASA

The favored theory about the birth of supermassive black holes up to now has been the "direct-collapse" theory. The theory proposes a solution to a cosmic riddle: Supermassive black holes seem to have been born a mere 690 million years after the Big Bang, not nearly long enough for the standard normal black hole genesis scenario to have played out, and on such a large scale. There are two versions of the direct-collapse theory.

One version proposes that if enough gas comes together in a supermassive gravitationally bound cloud, it can eventually collapse into a black hole, which, thanks the cosmic background-radiation-free nature of the very early universe, could then quickly pull in enough matter to go supermassive in a relatively short period of time.

According to astrophysicist Shantanu Basu of Western University in London, Ontario, this would only have been possible in the first 800 million years or so of the universe. "The black holes are formed over a duration of only about 150 million years and grow rapidly during this time," Basu told Live Science in the summer of 2019. "The ones that form in the early part of the 150-million-year time window can increase their mass by a factor of 10 thousand." Basu was lead author of research published last summer in Astrophysical Journal Letters that presented computer models showing this version of direct-collapse is possible.

Another version of the theory suggests that the giant gas cloud collapses into a supermassive star first, which then collapses into a black hole, which then — presumably again thanks to the state of the early universe — sucks up enough matter to go supermassive quickly.

There's a problem with either direct-collapse theory, however, beyond its relatively narrow time window. Previous models show it working only with pristine gas clouds comprised of hydrogen and helium. Other, heavier elements — carbon and oxygen, for example — break the models, causing the giant gas cloud to break up into smaller gas clouds that eventually form separate stars, end of story. No supermassive black hole, and not even a supermassive star for the second flavor of the direct-collapse theory.

A new model

ATERUI II

Image source: NAOJ

Japan's National Astronomical Observatory has a supercomputer named "ATERUI II" that was commissioned in 2018. The Tohoku University research team, led by postdoctoral fellow Sunmyon Chon, used ATERUI II to run high-resolution, 3D, long-term simulations to verify a new version of the direct-collapse idea that makes sense even with gas clouds containing heavy elements.

Chon and his team propose that, yes, supermassive gas clouds with heavy elements do break up into smaller gas clouds that wind up forming smaller stars. However, they assert that's not the end of the story.

The scientists say that post-explosion, there remains a tremendous inward pull toward the center of the ex-cloud that drags in all those smaller stars, eventually causing them to grow into a single supermassive star, 10,000 times larger than the Sun. This is a star big enough to produce the supermassive black holes we see when it finally collapses in on itself.

"This is the first time that we have shown the formation of such a large black hole precursor in clouds enriched in heavy-elements," says Chon, adding, "We believe that the giant star thus formed will continue to grow and evolve into a giant black hole."

Modeling the behavior of an expanded number of elements within the cloud while faithfully carrying forward those models through the violent breakup of the cloud and its aftermath requires such high computational overhead that only a computer as advanced as ATERUI II could pull off.

Being able to develop a theory that takes into account, for the first time, the likely complexity of early-universe gas clouds makes the Tohoku University idea the most complete, plausible explanation of the universe's mysterious supermassive black holes. Kazuyuki Omukai, also of Tohoku University says, "Our new model is able to explain the origin of more black holes than the previous studies, and this result leads to a unified understanding of the origin of supermassive black holes."