(CNN)About 600 million light-years away from Earth, the heartbeat of a supermassive black hole can be seen emanating from the center of a galaxy.
Astronomers first detected this signal, which repeats every hour, in 2007. Then, our sun blocked the black hole and its heartbeat from view by satellites in 2011.
When they were finally able to see it again in 2018 using the European Space Agency's XMM-Newton X-ray satellite, the scientists were amazed to see the heartbeat still going strong. Black hole heartbeats don't usually last very long.
The study published Tuesday in the journal Monthly Notices of the Royal Astronomical Society.
This black hole's heartbeat became the first one to be confirmed by scientists in 2007, and now it's the longest sustained heartbeat they've witnessed in a black hole.
This is an illustration of a black hole including the heartbeat signal observed both in 2007 and 2018.
Does a black hole really have a heartbeat?
Scientists refer to it as a heartbeat because the pulsating around the black hole creates a repetitive signal that can be detected. And the pulsating of this particular signal is sustained.
Although black holes themselves are invisible, the disk of material around them, called accretion disks, produce X-ray light that sensitive telescopes and satellites like XMM-Newton can detect.
Black holes feed off of material from the accretion disk, pulling spirals of gas inside that heat up. These high temperatures are what release the X-rays. So while black holes pull in material, at the same time they also release material in high-powered beams called jets.
The powerful force of the X-rays being released by this black hole in particular resemble the repetitive pattern of a heartbeat in the data they gathered. So far, this is rare in other black holes.
The time between the steady pulsating of this black hole can tell astronomers about the size and structure of the matter nearest to the black hole's event horizon--that's the area where not even light can escape the black hole's gravitational pull.
The astronomers compared the heartbeat to "feeding a toddler — go too fast and they burp it out," said Chris Done, study coauthor and professor of physics in Durham University's Centre for Extragalactic Astronomy, in an email.
"The main idea for how this heartbeat is formed is that the inner parts of the accretion disc are expanding and contracting," Done said in a statement. "The only other system we know which seems to do the same thing is a 100,000 times smaller stellar-mass black hole in our Milky Way."
This other black hole is located out in one of the spiral arms of our galaxy, Done said — it's not the supermassive black hole at the center of our galaxy. Instead, it is the remains of a very massive star which collapsed to form a black hole that is only about 10 times the mass of our sun, and it's being fed by matter from a binary companion star.
Although it's much smaller than the black hole in their study, "the rate at which it's being fed relative to the black hole mass is the same as in the object we were looking at, and it's unusually high," Done said.
Forceful signals
Compared to when the astronomers were able to observe the black hole's heartbeat initially, they noticed some changes to it during the 2018 observations.
"It got stronger, so we could see it more easily," Done said. "This meant we could examine its properties in more detail and see how similar it really is to the black hole binary we see in our galaxy."
Next, the researchers will conduct a full analysis of the heartbeat signal and compare it to the way that some black holes behave in our galaxy.
"This heartbeat is amazing," said Chichuan Jin, lead study author and researcher at the National Astronomical Observatories, Chinese Academy of Sciences, in a statement.
"It proves that such signals arising from a supermassive black hole can be very strong and persistent. It also provides the best opportunity for scientists to further investigate the nature and origin of this heartbeat signal."
