Intermediate-mass black holes devour stars like messy toddlers

A groundbreaking study led by Northwestern University has uncovered fascinating insights into the behavior of intermediate-mass black holes. These cosmic entities seem to exhibit a behavior akin to messy toddlers, as they consume wayward stars in a violent and erratic manner.

Using state-of-the-art 3D computer simulations, astrophysicists meticulously modeled black holes of varying masses and launched stars similar in size to our sun past them to observe the ensuing interactions. What they discovered was truly remarkable.

As a star approaches an intermediate-mass black hole, it becomes ensnared in the black hole’s orbit. Instead of an instant, catastrophic collision, the black hole engages in a prolonged and tumultuous feast. During each lap around the black hole, the star gets devoured a little more, as the black hole takes a bite with each passage.

The result of this celestial feast is an eventual reduction of the star to nothing but its incredibly dense core, misshapen and stripped of its former glory. At this critical point, the black hole ejects the remains, and the star’s remnant goes hurtling safely across the galaxy.

Apart from providing insights into the enigmatic behavior of intermediate-mass black holes, these simulations offer astronomers a new perspective on how to detect these hidden giants within our vast universe. Since black holes do not emit light, astronomers must rely on their interactions with the environment. The simulations show that stars undergoing multiple passages experience mass loss, causing them to flare up brightly as they are torn apart. Each flare becomes more luminous than the last, leaving a distinct signature that could aid in locating these elusive celestial behemoths amidst the stars.

The study’s lead researcher, Northwestern’s Fulya Kıroğlu, explains that the intricate dance between black holes and their surroundings might hold the key to unlocking the mysteries of these dark cosmic entities, allowing us to comprehend their elusive nature and place in the grand cosmos.

Watch an intermediate-mass black hole take a bite of a wayward star and then fling the leftovers across the galaxy. Credit: Fulya Kıroğlu/Northwestern University

Kıroğlu is set to present this groundbreaking research at the virtual portion of the American Physical Society’s (APS) April meeting, and The Astrophysical Journal has accepted the study for publication, underscoring its significance in the scientific community.

While lower- and higher-mass black holes have been confirmed by astrophysicists, the existence of intermediate-mass black holes has remained a mystery. These elusive entities are born from the collapse of supernovae and are estimated to be about 3 to 10 times the mass of our sun. On the other end of the cosmic scale, supermassive black holes, residing at the centers of galaxies, possess masses ranging from millions to billions of times that of our sun.

Should intermediate-mass black holes exist, they would fall in between these two extremes, with masses ranging from 10 to 10,000 times that of stellar remnant black holes but still significantly smaller than supermassive black holes. Despite strong theoretical predictions about their existence, astrophysicists have yet to find concrete observational evidence to support it.

The ongoing search for these intermediate-mass black holes is vital, as their discovery could provide crucial insights into the universe’s evolution and shed light on the formation and behavior of black holes across various size ranges. As astronomers continue their quest to locate these elusive cosmic objects, Kıroğlu’s research brings us one step closer to unraveling the secrets of these enigmatic entities in the vast expanse of space.

A star (bright orange dot on right) flying across the galaxy after being ejected from an intermediate-mass black hole (small ring on left). Credit: Fulya Kiroglu/Northwestern University

According to Kıroğlu, the existence of intermediate-mass black holes is still a topic of debate among astrophysicists. While some evidence points to their presence, alternative explanations, such as the accumulation of stellar-mass black holes, often challenge these findings.

To delve into the behavior of these elusive objects, Kıroğlu and her team devised innovative hydrodynamic simulations. They created a star model composed of numerous particles and propelled it towards the black hole, meticulously calculating the gravitational forces acting on the particles during the star’s approach.

Through these simulations, they made a remarkable discovery: stars can orbit an intermediate-mass black hole up to five times before finally being ejected. With each revolution, the star undergoes a gradual mass loss as it gets torn apart. The black hole then flings the remnants, moving at astonishing speeds, back into the galaxy. This repeating cycle generates a spectacular light display, providing astronomers with a potential clue to recognize and verify the existence of these enigmatic intermediate-mass black holes.

Kıroğlu emphasized the astonishing fact that some stars might survive the event, not entirely torn apart. These lucky survivors could be identified as hyper-velocity stars, which have been previously observed at the centers of galaxies.

The next step in their research involves simulating various types of stars, such as giant stars and binary stars, to explore how they interact with black holes. This ongoing investigation promises to shed more light on the elusive nature of intermediate-mass black holes and advance our understanding of the celestial wonders that shape our universe.

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