Study reveals that intermediate-mass black holes trap stars and “eat” them by ejecting leftovers
The black holes of intermediate mass, if they exist, probably devour rebel stars taking a few “bites” and then flinging the remains across the galaxy, say the authors of a new study led by Northwestern University (USA) and published in. The Astrophysical Journal.
In new 3-D computer simulations, astrophysicists modeled black holes of different masses and launched stars (the size of our Sun) in its path to see what was happening.
They discovered that, when a star approaches an intermediate-mass black hole, is trapped in its orbit. Then, the black hole begins its long and violent meal. Each time the star turns around, the black hole takes a bite out of it, cannibalizing the star even more with each pass.
At the end, only the deformed core remains incredibly dense core of the star. At that point, the black hole ejects the debris. The star’s debris flies to safety across the galaxy.
Unknown behavior
These new simulations not only point to unknown behaviors of intermediate-mass black holes, but they also provide astronomers with new clues to help finally locate these hidden giants in our night sky.
“Obviously, we cannot observe black holes directly because they don’t emit light,” explains Fulya Kiroglu of Northwestern, who led the study. So instead, we have to look at the interactions between black holes and their environments.
“We discovered that stars undergo multiple passages before being expelled,” he continues. After each passage, lose more masscausing a flare of light as they tear apart. Each flare is brighter than the previous one, creating a signature that could help astronomers find them.”
Kiroglu, a graduate student in astrophysics at Northwestern’s Weinberg College of Arts and Sciences and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), has presented the study at the American Physical Society (APS) meeting.
Have remained elusive
Although astrophysicists have demonstrated the existence of lower- and higher-mass block holes, intermediate-mass black holes have remained elusive. Created when supernovae collapse, stellar remnant black holes have between 3 and 10 times the mass of our sun. At the other end of the spectrum, supermassive black holes, which lurk at the center of galaxies, are millions to billions of times the mass of our sun.
If they did exist, intermediate-mass black holes would would be located at an intermediate point: 10 to 10,000 times more massive than stellar remnant black holes, but nowhere near as massive as supermassive black holes. Although such intermediate-mass black holes should exist in theory, astrophysicists have not yet found evidence irrefutable observational evidence.
“Their presence is still subject of debate -says Kiroglu. Astrophysicists have discovered evidence that they exist, but that evidence can often be explained by other mechanisms. For example, what appears to be an intermediate-mass black hole could actually be the black hole accretion of stellar mass”.
To explore the behavior of these elusive objects, Kiroglu, Frederic Rasio, Joseph Cummings Joseph Cummings Professor of Physics and Astronomy at Weinberg and CIERA member and co-author of the paper, and his team developed new hydrodynamic simulations.
Gravitational force
First, they created a model star, made up of many particles. Then, they sent the star toward the black hole and calculated the gravitational force acting on the particles during the approach of the star. “We can calculate specifically which particle is attached to the star and which particle is perturbed (or no longer attached to the star),” says Kiroglu.
Through these simulations, Kiroglu and his team discovered that stars. could orbit a black hole of intermediate mass up to five times before finally being ejected. At each revolution around the black hole, the star loses more and more mass as it is torn apart.
Next, the black hole ejects the debrismoving at blazing speeds, back into the galaxy. This repetitive pattern would create an impressive light show that would help astronomers recognize-and prove-the existence of intermediate-mass black holes.
“It is striking that the star is not completely torn apart -acknowledges Kiroglu-. Some stars might get lucky and survive the event. The ejection velocity is so high that these stars could be identified as hypervelocity stars, which have been observed in the centers of galaxies.”
Next, Kiroglu plans to simulate different types of stars, including giant stars and binary stars, to explore their interactions with black holes.
