#direct collapse

Sorry Science Fans, Discovering A 70-Solar-Mass Black Hole Is Routine, Not Impossible

“Astronomers aren't perplexed by this object (or similar ones to it) at all, but rather are fascinated with uncovering the details of how they formed and how common they truly are. The mystery isn't why these objects exist at all, but rather how the Universe makes them in the abundances we observe. We don't falsely generate excitement by spreading misinformation that diminishes our knowledge and ideas prior to this discovery.

In science, the ultimate rush comes from discovering something that furthers our understanding of the Universe within the context of everything else we know. May we never be tempted to pretend anything else is the case.”

Did you hear about this “impossible” black hole that “perplexes” astronomers and “defies” theory? If you followed the news cycle last week, that’s probably what you’ve heard. But the truth is far more interesting, and includes facts like:

-this is the fourth black hole we’ve found like it, not the first, -there are two other ways to make black holes that would explain this object in addition to the one way that can’t, -and that we’ve seen each and every one of the steps necessary to make a black hole like this, -but that finding this black hole with this particular method really is revolutionary?

What Was It Like When The First Stars Died?

“It's theorized that this is the origin of the seeds of the supermassive black holes that occupy the centers of galaxies today: the deaths of the most massive stars, which create black holes hundreds or thousands of times the mass of the Sun. Over time, mergers and gravitational growth will lead to the most massive black holes known in the Universe, black holes that are millions or even billions of times the mass of the Sun by today.

It took perhaps 100 million years to form the very first stars in the Universe, but just another million or two after that for the most massive among them to die, creating black holes and spreading heavy, processed elements into the interstellar medium. As time goes on, the Universe, at long last, will begin to resemble what we actually see today.”

Our Universe, shortly after the Big Bang, proceeded in a number of momentous steps. The first atomic nuclei formed just minutes after the Big Bang, while neutral atoms took hundreds of thousands of years. It took another 50 to 100 million years for the very first star to be created, but only, perhaps, a million or two years for the most massive among the first stars to die. They may have been short-lived, but the first stars were truly spectacular, and their deaths set up the first steps in a changing Universe that would take us from a pristine set of materials to, eventually, the Universe as we know it today.

'Direct Collapse' Black Holes May Explain Our Universe's Mysterious Quasars

“In a theoretical study published in March of this year, a fascinating mechanism for producing direct collapse black holes from a mechanism like this was introduced. A young, luminous galaxy could irradiate a nearby partner, which prevents the gas within it from fragmenting to form tiny clumps. Normally, it's the tiny clumps that collapse into individual stars, but if you fail to form those clumps, you instead can just get a monolithic collapse of a huge amount of gas into a single bound structure. Gravitation then does its thing, and your net result could be a black hole over 100,000 times as massive as our Sun, perhaps even all the way up to 1,000,000 solar masses.”

Some of the most distant, luminous objects in our entire Universe, quasars, are a mystery. How does our Universe get an active, supermassive black hole that forms so early, especially given how relatively small the stars that make black holes are known to be? Even given the earliest, most massive stars that can theoretically form, you’d only expect seed black holes of a few hundred solar masses, yet these early quasars have almost a billion Suns worth of mass to begin with. You’d need a seed 1,000 times as massive to get there. Well, that’s exactly what the scenario known as ‘direct collapse’ could get you. If a massive galaxy is close by another cloud of gas, it can suppress the formation of stars all while that cloud collapses, potentially leading to a black hole directly, without any stars. That black hole could be up to a million solar masses, providing a path to the earliest quasars with no further hitches. With the technology coming online in the next few years, we might yet see this process in action for the first time.

Surprise! The Universe Has A Third Way To Form Black Holes

“If a massive enough gas cloud collapses under its own gravity, it should form a black hole directly, without any intervening star. This is one of the leading theories for how supermassive black holes begin, including at such early times in the ultra-distant Universe.”

Everyone knows the recipe for a black hole: create a massive enough star, allow it to burn through the fuel it its core, and wait. After enough time, the core will collapse, creating a type II supernova and a runaway fusion reaction. The outer layers explode while the core implodes, leaving behind a black hole if it’s massive enough. Alternatively, merge two failed black holes -- i.e., neutron stars -- together, and you get a black hole, too. But there ought to be a third way: through direct collapse. We haven’t seen enough supernovae for the stars that exist, and we don’t have a great explanation, otherwise, for super-early supermassive black holes. For the first time ever, we’ve witnessed a massive star simply wink out of existence. We may have just caught a direct collapse black hole red-handed.

We schreven er eind mei al een blog over, maar vandaag is ’t dan officieel: het drietal sterrenkundigen Aaron Smith en Volker Bromm van de Universiteit van Texas in Austin en Avi Loeb van het Harvard-Smithsonian Center for Astrophysics hebben in het vaktijdschrift Monthly Notices of the Royal Astronomical Society het artikel gepubliceerd, waarin ze met het bewijs komen voor het bestaan van een nieuw soort zwart gat, het zogeheten ‘direct collapse’ zwart gat.

Evidence for a direct collapse black hole in the Lyman α source CR7

CR7 in de naam van de titel van het artikel is een sterrenstelsel, dat met de ESA/NASA Hubble ruimtetelescoop is waargenomen en dat 1 miljard jaar na de oerknal al voorkwam. Daar in dat vroege heelal moeten de omstandigheden precies goed zijn geweest om zwarte gaten te laten ontstaan via zo’n direct collapse, een manier die in het tegenwoordige heelal niet meer mogelijk is. Het bestaan van dergelijke zwarte gaten moet antwoord geven op de vraag hoe al zo vroeg in het heelal superzware zwarte gaten konden ontstaan, een vraag waar sterrenkundigen al lang mee worstelen. Ontstaan ze omdat kleinere zwarte gaten bij elkaar komen, samensmelten en dan steeds zwaardere zwarte gaten vormen? Nee, dat kan het niet zijn, want simulaties laten zien dat dat te veel tijd kost. Maar hoe kunnen ze dan wel ontstaan? Enter direct collapse black holes!

CR7, oh wacht da’s niet het sterrenstelsel CR7. Er zijn concurrerende sterren.

Het begint volgens Smith, Bromm en Loeb met een gigantische wolk van waterstof en helium. Normaal koelt zo’n wolk af, condenseert en fragmenteert tot losse sterren. Maar het vroege heelal was doordrenkt door een grote hoeveelheid hete ultraviolette straling, straling die niet alleen zorgt voor de reïonisatie van het heelal, maar die ook voorkomt dat de wolk afkoelt. Gevolg is dat de wolk krimpt, niet fragmenteert in afzonderlijke sterren, maar in zeer korte tijd ineen klapt tot een zwaar zwart gat. in CR7 heeft men nu met Hubble een zogeheten Lyman-alpha lijn in het spectrum gevonden, die uitgezonden is door het waterstof in het sterrenstelsel en die alleen kan zijn ontstaan in een bad van hete UV-straling, zo’n 100.000 K. Simulaties van theoretische en waargenomen spectra laten zien dat de waargenomen emissielijn alleen kan ontstaan door de snelle ineenstorting van een grote wolk tot een zwart gat, een direct collapse zwart gat dus. Bron: CfA.

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