New evidence suggests that the Universe began to form stars later than previously believed. This discovery may have given astronomers a clever new method of finding some of the earliest black holes. The research comes from Rennan Barkana from Tel Aviv University’s School of Physics and Astronomy and was published in Nature.
It was previously believed that gas in the Universe first heated and formed stars about 200 million years after the Big Bang. Now, new research suggests that it could have actually been closer to 400 million years. Because the heavier elements were formed in the core of stars, the earliest stars were made almost solely of hydrogen. As the first stars died, they emitted the hydrogen out into the Universe which can be detected through radio waves.
The expansion of the Universe has stretched and distorted the light from the earliest stars - but astronomers have ways of correcting for this and actually viewing stars as they existed over 13 billion years ago. With the stars forming slightly later than was previously thought, the light does not need to travel quite as far and scientists might have an easier time of viewing these extraordinary relics. Under the previous time constraints, it was assumed that the first stars are too distant to image. The “cosmic heating” that created the first stars could also be used to identify the first black holes.
It is believed that the first black holes were formed by some of the first stellar binary systems. When one star dies into a supernova, it likely stripped mass from its companion star, forming and feeding the black hole. As the other star gets sucked in by the gravity, high-energy radiation is spewed out. As it travels across the Universe, the radiation might have re-energized some of the hydrogen gas that had already cooled.
Understanding this re-heating process has allowed the researchers to not only alter the timeline of the early Universe, but also gave them an avenue to exploit the process to detect those earliest black holes. As the x-ray radiation from the destroyed companion star re-heated gas, radio waves were generated. By knowing what to look for, and more specifically when to look, astronomers might just be able to image the first stellar bodies and black holes.