Hello Space Fans and welcome to another edition of Space Fan News. This week a group of astronomers think they’ve figured out how supermassive black holes billions of times the mass of our Sun could have formed in the early universe; dark matter appears to have less influence on galaxy rotation in the early universe; and astronomers have observed a star orbiting a black hole at a distance of less than three times the distance of the Earth and the Moon.
Most of you by now know what a supermassive black hole is, they are black holes that measure in the hundreds of billions of solar masses and they are usually nestled at the centers of most galaxies in the universe.
Now ordinary 100 billion solar mass black holes that we see in nearby galaxies today form over a period of a billions of years, and they grow by merging with other galaxies supermassive black holes, devouring stars, gas, dust and anything and everything that gets too close. The fact that they take a lot of time makes intuitive sense, these sorts of mergers and interactions take a while and as the universe expands, they slowly become less frequent.
But what’s weird is that if that is how supermassive black holes are made, then how come we see them in the early universe too, when the the cosmos was only around 800 million years old? That is not enough time for supermassive black holes to form through collisions and mergers alone.
Well this week a new study released in the journal Nature Astronomy think they have an answer.
OK stay with me here, it’s gonna get weird.
Running computer simulations this team of astronomers have found that if an ancient galaxy has a black hole at its center and there is a nearby galaxy that is pushing out enough of its star forming gasses in such a way that prevent new stars from being born, in other words, all of the stars have strong enough stellar winds that pushes out all of its gas and dust - then the host galaxy (the one with the black hole) will suck up that gas and grow enough that it will eventually collapse forming a black hole that feeds on the remaining gas, and later, dust, dying stars, and possibly other black holes, to become super gigantic million solar mass black hole.
And get this, the time it takes for that galaxy to collapse and for the supermassive black hole form is only 100,000 years. From there only a few hundred million years need to pass to create a billion solar mass black hole.
So how can this happen? Remember that the stars in the early universe are not like the stars we see today. Most of them were formed from molecular hydrogen and are very large, very hot, very violent and very short lived stars. They only hung around for a few hundred million years at most with the majority lasting less than 100 million years.
It’s not too far fetched then to have a galaxy so full of these hot stars with stellar winds strong enough to stop all star formation inside that galaxy and kick out its gas to the black hole galaxy.
Now like most simulations, for this to work out, conditions need to be just right. The nearby galaxy can’t be too hot, or too cold, nor can it be too close or too far. But there are a lot of galaxies in the sky and the early universe was full of them too, so there only needs to be a few situations laid out like this for a supermassive black hole to form so early after the Big Bang. Astronomers haven’t found all that many so far anyway.
And as usual, we are all waiting for the James Webb Space Telescope to get to the L2 point in late 2018 to help us learn more about how supermassive black holes can exist in the early universe.
Next, while we on the topic of the early universe, it turns out that dark matter may have played less of a part in early galaxies than it does today.
For those who don’t know, dark matter is this highly annoying material that no one has observed directly yet because it won’t interact with us in any way. The only way we know it’s there is by looking at the effect it has on things we can see.
Now it’s easy to get annoyed at dark matter and say that we’re just making it up but look at this. This graph is a perfect example. On the right is a galaxy rotation curve from a normal, nearby spiral galaxy. The outer stars are rotating very fast, too fast if all that is there were stars, gas, dust and a supermassive black hole.
The graph on the right is exactly what you’d expect to see if there were no dark matter at all. As you can see, the outer stars are rotating slowly. And this is the rotation curves that were measured in a study that came out this week.
Astronomers using the European Southern Observatory’s Very Large Telescope measured the rotation rates of six massive, star-forming galaxies in the distant Universe, this was a period when galaxy formation was higher than it’s ever been, some 10 billion years ago.
They found that unlike spiral galaxies in the modern Universe, the outer regions of these distant galaxies seem to be rotating more slowly than regions closer to the core — which as I’ve just told you suggests there is less dark matter present than expected.
I’m sorry but I just gotta say it. That is Just Like Downtown. This result is important because apparently dark matter didn’t play a big role in galaxy evolution in the early universe. What may be going on here is that 3 to 4 billion years after the Big Bang, the gas in galaxies had already efficiently condensed into flat, rotating discs, while the dark matter halos surrounding them were much larger and more spread out. Apparently it took billions of years longer for dark matter to condense as well, so its dominating effect is only seen on the rotation velocities of galaxy discs today.
I feel like I need to come up with a galaxy rotation dance now…
Finally astronomers using NASA's Chandra X-ray Observatory as well as NASA's NuSTAR and the Australia Telescope Compact Array (ATCA) have found a star that is orbiting really, really close to a black hole.
The star is part of a binary in the globular cluster 47 Tucanae, a dense cluster of stars in our galaxy about 14,800 light years from Earth. You may remember that star cluster because I told you about astronomers finding a IMBH there in SFN 194.
While astronomers have observed this binary for many years, it wasn't until 2015 that radio observations with the ATCA revealed the pair likely contains a black hole pulling material from a companion star called a white dwarf, a low-mass star that has exhausted most or all of its nuclear fuel.
New Chandra data of this system, known as X9, show that it changes in X-ray brightness in the same manner every 28 minutes, which is likely the length of time it takes the companion star to make one complete orbit around the black hole.
This means that this white dwarf is so close to that black hole that it is going around twice every hour.
Chandra data also shows evidence for large amounts of oxygen in the system, which is a characteristic feature of white dwarfs. And so a strong case can therefore be made that the companion star is a white dwarf, and if that’s true, then it be orbiting the black hole at only about 2.5 times the separation between the Earth and the Moon.
Astronomers say this white dwarf is so close to the black hole that material is being pulled away from the star and dumped onto a disk of matter around the black hole before falling in. They also say that this star is in a pretty stable orbit and probably won’t fall in.
However so much matter may be pulled away from the white dwarf that it ends up only having the mass of a planet. If it keeps losing mass, the white dwarf may completely evaporate.
So how could such a thing come about? How can a star get so close and not fall in?
One possibility is that the black hole smashed into a red giant star, and then gas from the outer regions of the star was ejected from the binary. The remaining core of the red giant would form into a white dwarf, which becomes a binary companion to the black hole. The orbit of the binary would then have shrunk as gravitational waves were emitted, until the black hole started pulling material from the white dwarf.
An alternative explanation for the observations is that the white dwarf is partnered with a neutron star, rather than a black hole. In this scenario, the neutron star spins faster as it pulls material from a companion star via a disk, a process that can lead to the neutron star spinning around its axis thousands of times every second. A few such objects, called transitional millisecond pulsars, have been observed near the end of this spinning up phase.
He astronomers in this study don’t think this happened though because transitional millisecond pulsars have properties that aren’t seen in X9, such as extreme variability at X-ray and radio wavelengths.
Still, they can’t disprove this explanation either.
Man, that planet in ‘Interstellar’ has nothing on this place. Can you imagine how weird it must be there?
Well that’s it for this week Space Fans. We had a really great discussion on Wednesday about the future of SFN so thanks for taking part, if you couldn’t make it, please leave comments on that video and I’ll still keep checking them. Let’s plan on a follow up LIVE Event in two weeks to gather what we’ve learned and make a plan.
Thanks to all Patreon Patrons for making SFN possible, this is your show and you are crucial to these episodes. Thanks to all of you for watching and as always, Keep Looking Up!