Medium-sized black holes eat stars like messy toddlers
Elusive intermediate-mass black holes take a few bites, then eject the leftovers

Date:
April 25, 2023
Source:
Northwestern University
Summary:
In new 3D computer simulations, astrophysicists modeled black holes
of varying masses and then hurled stars (about the size of our sun)
past them to see what might happen. If they exist, intermediate-mass
black holes likely devour wayward stars like a messy toddler --
taking a few bites and then flinging the remains across the galaxy.


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FULL STORY ==========================================================================
If they exist, intermediate-mass black holes likely devour wayward stars
like a messy toddler -- taking a few bites and then flinging the remains
across the galaxy -- a new Northwestern University-led study has found.

In new 3D computer simulations, astrophysicists modeled black holes of
varying masses and then hurled stars (about the size of our sun) past
them to see what might happen.

When a star approaches an intermediate-mass black hole, it initially
gets caught in the black hole's orbit, the researchers discovered. After
that, the black hole begins its lengthy and violent meal. Every time the
star makes a lap, the black hole takes a bite -- further cannibalizing
the star with each passage. Eventually, nothing is left but the star's misshapen and incredibly dense core.

At that point, the black hole ejects the remains. The star's remnant
flies to safety across the galaxy.

Not only do these new simulations hint at the unknown behaviors of intermediate-mass black holes, they also provide astronomers with new
clues to help finally pinpoint these hidden giants within our night sky.

"We obviously cannot observe black holes directly because they don't
emit light," said Northwestern's Fulya Kıroğlu, who led the
study. "So, instead, we have to look at the interactions between black
holes and their environments. We found that stars undergo multiple
passages before being ejected. After each passage, they lose more mass,
causing a flair of light as its ripped apart. Each flare is brighter than
the last, creating a signature that might help astronomers find them." Kıroğlu will present this research during the virtual portion
of the American Physical Society's (APS) April meeting. "Tidal disruption events of stars by intermediate-mass black holes" will take place on April
25, as a part of the session "Medium: Cosmic Rays, AGN & Galaxies." . The Astrophysical Journal has accepted the study for publication.

Kıroğlu is an astrophysics graduate student at Northwestern's Weinberg College of Arts and Sciences and member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). She is advised by paper co-author Frederic Rasio, the Joseph Cummings Professor
of Physics and Astronomy at Weinberg and member of CIERA.

While astrophysicists have proven the existence of lower- and higher-mass
block holes, intermediate-mass black holes have remained elusive. Created
when supernovae collapse, stellar remnant black holes are about 3
to 10 times the mass of our sun. On the other end of the spectrum,
supermassive black holes, which lurk in the centers of galaxies, are
millions to billions times the mass of our sun.

Should they exist, intermediate-mass black holes would fit somewhere in
the middle -- 10 to 10,000 times more massive than stellar remnant black
holes but not nearly as massive as supermassive black holes. Although
these intermediate- mass black holes theoretically should exist, astrophysicists have yet to find indisputable observational evidence.

"Their presence is still debated," Kıroğlu
said. "Astrophysicists have uncovered 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 might actually be
the accumulation of stellar-mass black holes." To explore the behavior
of these evasive objects, Kıroğlu and her team developed
new hydrodynamic simulations. First, they created a model of a star,
consisting of many particles. Then, they sent the star toward the black
hole and calculated the gravitational force acting on the particles
during the star's approach.

"We can calculate specifically which particle is bound to the star
and which particle is disrupted (or no longer bound to the star)," Kıroğlu said.

Through these simulations, Kıroğlu and her team discovered
that stars could orbit an intermediate-mass black hole as many as five
times before finally being ejected. With each pass around the black hole,
the star loses more and more of its mass as its ripped apart. Then, the
black hole kicks the leftovers -- moving at searing speeds -- back out
into the galaxy. The repeating pattern would create a stunning light show
that should help astronomers recognize -- and prove the existence of -- intermediate-mass black holes.

"It's amazing that the star isn't fully ripped apart," Kıroğlu
said.

"Some stars might get lucky and survive the event. The ejection speed
is so high that these stars could be identified as hyper-velocity
stars, which have been observed at the centers of galaxies." Next, Kıroğlu plans to simulate different types of stars, including
giant stars and binary stars, to explore their interactions with black
holes.

* RELATED_TOPICS
o Space_&_Time
# Black_Holes # Stars # Galaxies # Astronomy #
Astrophysics # Solar_Flare # Extrasolar_Planets #
Northern_Lights
* RELATED_TERMS
o Red_supergiant_star o Supergiant o Gravitational_wave o Galaxy
o Geosynchronous_orbit o Globular_cluster o General_relativity
o Barred_spiral_galaxy

========================================================================== Story Source: Materials provided by Northwestern_University. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Fulya Kıroğlu, James C. Lombardi Jr., Kyle Kremer, Giacomo
Fragione, Shane Fogarty, Frederic A. Rasio. Tidal Disruption of
Main- Sequence Stars by Intermediate-Mass Black Holes. submitted
to arXiv, 2023 DOI: 10.48550/arXiv.2210.08002 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/04/230425205336.htm

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