Scientists discover first 'intermediate-mass' black hole in massive merger

It's the largest black hole merger ever observed by scientists.

Black hole
Credit: Pixabay
  • In 2019, scientists detected gravitational waves that were later determined to come from the merging of two so-called "intermediate-mass" black holes.
  • These black holes were thought to exist, but had never been directly observed.
  • The discovery sheds new light on how black holes form.

In May 2019, a ripple of gravitational waves passed through Earth after traveling across the cosmos for 7 billion years. The ripple came in four waves, each lasting just a fraction of a second. Although the ancient signal was faint, its source was cataclysmic: the biggest merger of two black holes ever observed.

It occurred when two mid-sized black holes — 66 and 85 times the mass of our Sun — drifted close together, began spinning around each other and merged into one black hole roughly 142 times the mass of our Sun.

"It's the biggest bang since the Big Bang observed by humanity," Caltech physicist Alan Weinstein, who was part of the discovery team, told The Associated Press.

A massive bang, sure. But a black hole of this size actually falls within the "intermediate-mass" category, which ranges from about 50 to 1,000 times the mass of our Sun.

Intermediate-mass black holes

Scientists know relatively little about these mid-sized black holes. They've catalogued small black holes only a few times more massive than the Sun, as well as supermassive black holes more than six billion times the mass of our star. But direct evidence of intermediate-mass black holes has remained elusive.

"Long have we searched for an intermediate-mass black hole to bridge the gap between stellar-mass and supermassive black holes," Christopher Berry, a professor at Northwestern University's Center for Interdisciplinary Exploration and Research in Astrophysics), told Northwestern Now. "Now, we have proof that intermediate-mass black holes do exist."

Still, how these middleweight black holes form is a mystery. Scientists know that smaller black holes form when stars explode in violent events called supernovas. But mid-sized black holes couldn't form this way, according to current physics, because stars of a certain mass range undergo a death process called pair instability, where they explode and leave nothing behind, not even a black hole.

LIGO-Virgo

This chart compares the mass of black-hole merger events observed by LIGO-Virgo.

Credit: LIGO/Caltech/MIT/R. Hurt (IPAC)

As for supermassive black holes? Scientists are pretty sure that these behemoths, which lie in the center of most galaxies, grow huge by gobbling up ancient dust, gas and other cosmic matter — including other black holes. Intermediate black holes may form in a similar way, by small-ish black holes repeatedly merging together.

In other words, an intermediate black hole might be on its way to becoming supermassive.

"We're talking here about a hierarchy of mergers, a possible pathway to make bigger and bigger black holes," Martin Hendry, a professor of gravitational astrophysics and cosmology at Glasgow University, told the BBC. "So, who knows? This 142-solar-mass black hole may have gone on to have merged with other very massive black holes — as part of a build-up process that goes all the way to those supermassive black holes we think are at the heart of galaxies."

Black hole

Visualization of a black hole.

Credit: NASA

The recent discovery sheds light on how black holes form, but questions still remain. Scientists with the LIGO-Virgo collaboration hope to continue studying the newly discovered intermediate black hole — dubbed GW190521 — in 2021 when the facilities will be up and running again with improved instruments.

"Our ability to find a black hole a few hundred kilometers-wide from half-way across the Universe is one of the most striking realizations of this discovery," Karan Jani, an astrophysicist with LIGO told The Malaysian Reserve.

The discovery was described in two papers published in the Physical Review Letters and The Astrophysical Journal Letters.

This is what aliens would 'hear' if they flew by Earth

A Mercury-bound spacecraft's noisy flyby of our home planet.

Image source: sdecoret on Shutterstock/ESA/Big Think
Surprising Science
  • There is no sound in space, but if there was, this is what it might sound like passing by Earth.
  • A spacecraft bound for Mercury recorded data while swinging around our planet, and that data was converted into sound.
  • Yes, in space no one can hear you scream, but this is still some chill stuff.

First off, let's be clear what we mean by "hear" here. (Here, here!)

Sound, as we know it, requires air. What our ears capture is actually oscillating waves of fluctuating air pressure. Cilia, fibers in our ears, respond to these fluctuations by firing off corresponding clusters of tones at different pitches to our brains. This is what we perceive as sound.

All of which is to say, sound requires air, and space is notoriously void of that. So, in terms of human-perceivable sound, it's silent out there. Nonetheless, there can be cyclical events in space — such as oscillating values in streams of captured data — that can be mapped to pitches, and thus made audible.

BepiColombo

Image source: European Space Agency

The European Space Agency's BepiColombo spacecraft took off from Kourou, French Guyana on October 20, 2019, on its way to Mercury. To reduce its speed for the proper trajectory to Mercury, BepiColombo executed a "gravity-assist flyby," slinging itself around the Earth before leaving home. Over the course of its 34-minute flyby, its two data recorders captured five data sets that Italy's National Institute for Astrophysics (INAF) enhanced and converted into sound waves.

Into and out of Earth's shadow

In April, BepiColombo began its closest approach to Earth, ranging from 256,393 kilometers (159,315 miles) to 129,488 kilometers (80,460 miles) away. The audio above starts as BepiColombo begins to sneak into the Earth's shadow facing away from the sun.

The data was captured by BepiColombo's Italian Spring Accelerometer (ISA) instrument. Says Carmelo Magnafico of the ISA team, "When the spacecraft enters the shadow and the force of the Sun disappears, we can hear a slight vibration. The solar panels, previously flexed by the Sun, then find a new balance. Upon exiting the shadow, we can hear the effect again."

In addition to making for some cool sounds, the phenomenon allowed the ISA team to confirm just how sensitive their instrument is. "This is an extraordinary situation," says Carmelo. "Since we started the cruise, we have only been in direct sunshine, so we did not have the possibility to check effectively whether our instrument is measuring the variations of the force of the sunlight."

When the craft arrives at Mercury, the ISA will be tasked with studying the planets gravity.

Magentosphere melody

The second clip is derived from data captured by BepiColombo's MPO-MAG magnetometer, AKA MERMAG, as the craft traveled through Earth's magnetosphere, the area surrounding the planet that's determined by the its magnetic field.

BepiColombo eventually entered the hellish mangentosheath, the region battered by cosmic plasma from the sun before the craft passed into the relatively peaceful magentopause that marks the transition between the magnetosphere and Earth's own magnetic field.

MERMAG will map Mercury's magnetosphere, as well as the magnetic state of the planet's interior. As a secondary objective, it will assess the interaction of the solar wind, Mercury's magnetic field, and the planet, analyzing the dynamics of the magnetosphere and its interaction with Mercury.

Recording session over, BepiColombo is now slipping through space silently with its arrival at Mercury planned for 2025.

Photo by Martin Adams on Unsplash
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Credit: Helen_f via AdobeStock
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