Black holes are amazing celestial objects. Gravity is too strong Nothing, not even light, can escape it. The most massive black holes, known as “supermassive” black holes, can have masses ranging from millions to billions of times that of the Sun.
These giants Usually lives in the center of the galaxy. Our galaxy, the Milky Way, Contains a supermassive black hole In that heart too.
So how does this supermassive black hole become a supermassive black hole? To answer this question, Our teamAstrophysicists’ We look back over 13.8 billion years of universe history to trace how supermassive black holes have grown from their inception to the present day.
We built a model Overall growth history A supermassive black hole that has existed for the past 12 billion years.
How do supermassive black holes grow?
Supermassive black holes grow in two main ways: They can consume gas from their host galaxy. A process called adsorptionAnd they can also merge with each other When two galaxies collide.
Artist’s drawing of an accreting supermassive black hole. The central black hole is black, while the surrounding gas is heated and glows. (Source: Nahks Tr’Ehnl (Penn State))
When a supermassive black hole consumes gas, Almost always emits strong X-raysIt’s a high-energy light that’s invisible to the naked eye. You’ve probably seen X-rays at the dentist. Sometimes, dentists use X-rays to examine your teeth. X-rays used by astronomers They are generally lower energy than medical X-rays.
So how can any light, even invisible X-rays, escape a black hole? Strictly speaking, light does not come from the black hole itself, but from the gas just outside. As the gas is pulled into the black hole, it heats up and glows, emitting X-rays. The more gas a supermassive black hole consumes, the more X-rays it produces.
Thanks to over 20 years of data from three of the most powerful X-ray facilities ever launched into space – Chandra, XMM-Newtonand Eroshita– Astronomers can detect X-rays from many of the supermassive black holes that exist in the universe.
With this data, our research team can estimate how fast supermassive black holes grow by consuming gas. On average, supermassive black holes are about mass of the sun The exact value each year varies depending on many factors.
for example, The data shows The growth rate of a black hole is averaged over millions of years and is closely related to the mass of all the stars in the parent galaxy.
How often do supermassive black holes merge?
In addition to absorbing gas, supermassive black holes can also grow by merging with other galaxies when they collide, forming a single, more massive black hole.
Supercomputer Cosmology Simulations It is possible to predict how often such events occur. These simulations aim to model how the universe grows and evolves over time. The countless galaxies flying through space are like bricks that build up the universe.
these Simulation Results Galaxies and the supermassive black holes within them may have merged multiple times throughout the history of the universe.
Our team used X-rays and supercomputer simulations to track these two growth channels—gas consumption and mergers—and then combined them to construct an overall growth history that maps the growth of black holes across the universe over billions of years.
Our growth history is revealed Billions of years ago, when the universe was young, supermassive black holes grew much faster.
In the early days of the universe, there was more gas than the supermassive black holes could consume, and supermassive black holes continued to form. As the universe grew older, the gas gradually ran out, and the growth of supermassive black holes slowed. About 8 billion years ago, the number of supermassive black holes stabilized. Since then, it has not increased much.
Illustration of two supermassive black holes merging. Scott Noble (Source: NASA GSFC)
When there is not enough gas for a supermassive black hole to grow by accretion, the only way for a black hole to grow is through mergers. We have not seen many such cases in the history of growth. On average, the most massive black holes can accumulate mass through mergers at a rate of about the mass of the Sun every few decades.
expect
The study helped us understand how more than 90 percent of the black hole’s mass was accumulated over the past 12 billion years.
However, we still need to investigate how they grew. The very early universe We are trying to explain the remaining few percent of the black hole’s mass. The astronomy community is making progress in exploring these early supermassive black holes, and we hope to find more answers soon.
Fan Zou is a graduate student in astronomy and astrophysics at Penn State. W. Niel Brandt is a professor of astronomy and astrophysics at Penn State. This article was republished from conversation ~Below Creative Commons License. read Original article.
