How long have black holes been around for?

Answer 1

Black holes have been around since the big bang.

After the the Big Bang about 13.7 billion years ago, there was nothing of any significance happening for the first 350 million years as the universe was still so dense that it was not even transparent. As it continued to expand it broke out of this dense cloud and began to collect into areas that would eventually become galaxies from incredibly small quantum fluctuations in the initial energy that exploded out of the original cosmic "seed." these infinitesimal changes in the original structure of the expanding universe were the basis for the eventual structures we see today in every direction around us today. Yet the evidence going from the emergence of the visible universe (350 million years after the Big Bang) to the creation of the first galaxies is really not fully understood even today.

The fact is that the universe was so dense, and the amount of hydrogen generated by the Big Bang (about 75% of everything created from the Big Bang) was so much, that the first stars that came from this environment must have been huge. (Currently the largest star we can see and determine today is about 100 times larger then the size of our own sun.) Our sun is considered as a very average star in its size and temperature. In order to go from a star into a black hole the equation implies that the star must be at least 3 times the size of our sun. Yet most texts imply that it really must be as much as 10 times the size of the sun to insure it will go into a black hole configuration. Stars between these sizes will go into a more likely configuration as a neutron star.

So these huge first stars could have been incredibly large compared to what we see in the Universe today. Now we know that the larger the star, the faster it runs through its hydrogen fuel. Our Sun is about half way through its expected life. Its hydrogen has been used at a current rate of 400 million tons every second. Yet as far as we can tell the sun has another 5 billion years of fuel, even at that incredible amount required to maintain the sun's current configuration.

So considering that much larger stars use up their fuel faster due to the physics of the thermonuclear reaction of hydrogen to helium. Currently we have some huge stars that are visible today which will use their fuel and go supernova in as little as 60 million years compared to the 10 billion years of the average star. Therefore if the original first stars have been incredibly huge which means these stars did not last very long, burning up their hydrogen in only millions of years then almost all of these stars converted into black holes within millions of years beyond the 350 million years required to stabilize the Universe into a transparent environment.

Remember that the evidence is mounting that almost every galaxy in the universe has a "super massive" black hole in its center. Super massive implies at least a thousand times the mass of our Sun. Some are millions, even billions of times the mass of our Sun. The one at the center of our galaxy the Milky Way is thought to be about 3 - 4 million times the mass of our sun. With this kind of evidence there is a definite relationship between the creation of the galaxy and the super massive black hole in its center. Galaxies are see out to about 13 billion light years which implies they were created about 13 billion years ago. So sometime between 13.7 billion years for the Big Bang and 13 billion years for the creation of galaxies. That says that between 350 million years to universal transparency and 700 million years to galaxy formation is when the first black holes must have appeared.