Hunting for supermassive black holes in the early universe

Supermassive black holes (SMBHs)—black holes with plenty exceeding 1,000,000 instances that of the sun—are identified to prevail within the universe as we speak. Nevertheless, it isn’t clear but when, the place, and the way they shaped through the 13.8 billion years of cosmic historical past.

Observations previously few many years have revealed that each galaxy harbors a SMBH within the middle, and that the black hole mass is nearly all the time one-thousandth of the host galaxy mass. This shut relationship implies that galaxies and SMBHs have co-evolved collectively. Revealing the origin of SMBHs is thus essential not solely to grasp SMBHs themselves, but additionally to elucidate the formation processes of galaxies, the main constituents of the seen universe.

A key to addressing this problem lies within the early universe, the place the time elapse because the Large Bang (i.e., the start of the universe) was lower than a billion years. Due to the finite velocity of sunshine, we will look again on the previous by observing the distant universe. Did SMBHs exist already when the universe was solely a billion years outdated or much less? Is it potential for a black hole to amass such a big mass (exceeding 1,000,000 solar plenty and typically reaching billions of solar plenty) in such a short while? In that case, what are the underlying bodily mechanisms and circumstances?

So as to shut in on the origin of SMBHs, we have to observe them and examine their properties with predictions from theoretical models. And so as to take action, we first want to seek out the place they’re within the sky.

We used the Subaru Telescope on the prime of Maunakea, Hawaii, for the current examine. One of many greatest benefits of Subaru is its widefield observing functionality, which is especially fitted to our objective. Since SMBHs don’t emit gentle, we appeared for a particular class referred to as “quasars”—SMBHs with shining outskirts the place the infalling materials releases gravitational energy.

We noticed a large sky space equal to five,000 instances the full moon, and efficiently found 162 quasars residing within the early universe. Specifically, 22 of them lived within the period when the universe was lower than 800 million years outdated—essentially the most historical interval by which quasars have been acknowledged thus far.

The big variety of quasars we found has allowed us to find out essentially the most basic measure referred to as the “luminosity operate,” which describes the space density of quasars as a operate of radiation vitality. We discovered that quasars had been forming very quickly within the early universe, whereas the general form of the luminosity operate (aside from the amplitude) remained unchanged over time.

This attribute habits of the luminosity operate gives robust constraints on theoretical fashions, which might finally reproduce all of the observables and describe the origin of SMBHs. Our examine is revealed in The Astrophysical Journal Letters.

Then again, the universe was identified to have skilled a serious phase transition referred to as “cosmic reionization” in its early stage. Previous observations counsel that the entire intergalactic space was ionized on this occasion. The supply of the ionization vitality continues to be beneath debate, with radiation from quasars being thought of as a promising candidate.

By integrating the above luminosity operate, we discovered that quasars emit 10²⁸ photons per second in a unit quantity of 1 light-year on a facet within the early universe. That is lower than 1% of the photons wanted to keep up the ionized state of the intergalactic space at the moment, and thus signifies that quasars made solely a minor contribution to cosmic reionization. Different energy sources are critically wanted, which, in response to different latest observations, could be the built-in radiation from huge sizzling stars in forming galaxies.