(Web Desk) - Astronomers have spotted what may be a rare type of black hole hiding on the outskirts of a distant galaxy. This discovery could help fill in a key missing piece in our understanding of how black holes grow over time – and how galaxies build themselves around them.
The new object, known as NGC 6099 HLX-1, was picked up through a collaborative effort using NASA’s Hubble Space Telescope and the Chandra X-ray Observatory.
The bright X-ray signal coming from this object suggests it might belong to a hard-to-find class of black holes known as intermediate-mass black holes (IMBHs).
The suspected black hole is located within a compact star cluster about 40,000 light-years from the center of the galaxy NGC 6099. This galaxy lies approximately 450 million light-years away in the constellation Hercules.
Most galaxies have two kinds of black holes. The massive ones – millions to billions of times the mass of our Sun – are located in the center of galaxies. Then, there are the much smaller black holes – typically less than 100 times the Sun’s mass – formed from dying stars.
Between the smallest and largest black holes lies a largely uncharted middle ground: intermediate-mass black holes. Ranging from hundreds to hundreds of thousands of solar masses, they’ve been incredibly difficult to detect.
Unlike their larger cousins, IMBHs usually aren’t feeding. They don’t suck in enough material to glow brightly. Unless something triggers a flare – like a passing star getting too close – they remain invisible.
In this case, astronomers believe the black hole may have been caught red-handed during one of those feeding episodes, what scientists call a “tidal disruption event.” When a black hole tears apart a star, it creates a superheated disk of plasma that shines in X-rays.
Chandra first picked up the signal in 2009. ESA’s XMM-Newton observatory then tracked it over time. In 2012, the object reached peak brightness – about 100 times brighter than it was in 2009. Since then, the brightness has faded.
“If the IMBH is eating a star, how long does it take to swallow the star’s gas? In 2009, HLX-1 was fairly bright. Then in 2012, it was about 100 times brighter. And then it went down again,” noted study co-author Roberto Soria of the Italian National Institute for Astrophysics (INAF).
“So now we need to wait and see if it’s flaring multiple times, or there was a beginning, there was peak, and now it’s just going to go down all the way until it disappears.”