super huge black hole It is one of the most impressive and terrifying objects in the universe, with about a billion times more mass than the Sun. And we know it’s been around for a long time.
In fact, astronomers detected Extremely luminous compact sources located in the centers of galaxies known as quasars (rapidly growing supermassive black holes) when the universe was less than a billion years old.
Now our new research Astrophysical Journal LettersObservations from the Hubble Space Telescope were used to show that there were more (much less luminous) black holes in the early universe than previous estimates. Interestingly, this may help us understand how they formed and why many appear to be larger than expected.
Black holes grow by engulfing surrounding material in a process called accretion. This creates huge amounts of radiation. pressure caused by this radiation set fundamental limits About how fast a black hole can grow.
Scientists have therefore had a difficult time explaining these early giant quasars. Because there wasn’t much cosmic time to feed, quasars must have grown faster than was physically possible or were born incredibly massive.
light and heavy seeds
But how do black holes form? Several possibilities exist. The first is the so-called primordial black hole It has been in existence since shortly after. big bang. Although plausible for low-mass black holes, supermassive black holes cannot form in large quantities. standard model of cosmology.
Black holes can definitely form. gravitational waves astronomy) at the last stage Short lifespans of ordinary massive stars. Such black holes could, in principle, grow rapidly if they form in extremely dense clusters where stars and black holes can merge. It’s the “star mass seed” of a black hole that needs to grow so quickly.
The alternative is that they “heavy seeds“is about 1,000 times more massive than any known massive star. One such mechanism is “direct collapse,” in which the initial structure of the unknown, invisible material looks like this: dark matter Limited gas clouds and background radiation prevent stars from forming. Instead they collapsed into a black hole.
The problem is that only a few dark matter halos grow large enough to form such seeds. So this only works as an explanation if the initial black holes were sufficiently rare.
There are too many black holes
For many years we’ve had a good picture of how many galaxies existed in the first billion years of cosmic time. However, finding black holes in these environments has been extremely difficult (only luminous quasars can be proven).
Black holes grow by swallowing surrounding material, but this does not happen at a constant rate. Black holes change their brightness over time by dividing their prey into “meals.” We’ve monitored changes in the brightness of some of the earliest galaxies for 15 years and used this to take a new census of how many black holes there are in the universe.
It turns out that there are many times more black holes in a typical early galaxy than we originally thought.
Another pioneering work began recently with the James Webb Space Telescope (JSTW). to reach a similar conclusion. In total, we have more black holes than can form from direct collapse.
There is another, more exotic way to form black holes that can produce huge and abundant seeds. Stars are formed by the gravitational contraction of gas clouds. If a significant number of dark matter particles can be captured during the contraction phase, the internal structure may be Can be completely modified – and nuclear ignition is prevented.
Therefore, growth can continue for several times longer than the typical lifespan of a typical star, allowing it to become much more massive. But nothing can ultimately withstand the overwhelming force of gravity like a regular star or a directly collapsing object. This means that these “dark stars” should also eventually collapse and form massive black holes.
We now believe that a similar process must have occurred in the infant universe to form the numerous black holes we observe.
future plans
initial research black hole Formation has undergone changes over the past two years, but in some ways the field is just beginning.
New observatories in space such as Euclid’s mission or Nancy Grace Roman Space TelescopeIt will initially populate a census of fainter quasars. that New Athena Mission and square kilometer arrayEarly findings from Australia and South Africa will open up our understanding of many of the processes surrounding black holes.
But what we need to pay attention to right away is JWST. With its sensitivity for imaging and monitoring, and its spectroscopy ability to see very faint black hole activity, we expect that over the next five years we will be able to get a real picture of the number of black holes when the first galaxies formed.
We can also capture the black hole formation process by witnessing the explosions associated with the collapse of the first primordial stars. Models say this is possible, but it will require a collaborative and dedicated effort from astronomers.
Matthew J. HayesAssociate Professor, Department of Astrophysics, Stockholm University
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