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Space dance: UNM researchers track 2 supermassive black holes

Copyright © 2017 Albuquerque Journal

Karishma Bansal studies objects that are 4.5 sextillion miles from earth.

That’s 4,500,000,000,000,000,000,000 miles, to be exact.

The University of New Mexico graduate student in the physics and astronomy department and her colleagues made international news late last month after observing and measuring – for the first time – two supermassive black holes orbiting each other.

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Each one is the size of our solar system and moves at 4 million mph.

Black holes are an area of space where gravity is so strong that not even light can escape.

A research paper with Bansal as principal author was published in the July 1 issue of The Astrophysical Journal.

Two years ago, Bansal began studying data taken since 2003 from the Very Large Baseline Array radio telescope, based west of Socorro, using the information to plot points of the paths of the two black holes 750 million light-years away. One light-year is about 6 trillion miles.

“I didn’t know where it was headed and then – woohoo!” Bansal said of her work.

She had an idea of what to look for, though.

UNM professor of physics and astronomy Greg Taylor and graduate student Karishma Bansal recently observed and measured the orbital motion of two supermassive black holes. (Adolphe Pierre-Louis/Albuquerque Journal)

UNM professor and co-author Greg Taylor detected the system around 20 years ago during postdoctoral work at the California Institute of Technology.

Large galaxies, including the Milky Way, contain supermassive black holes at their centers.

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After finding two black holes in the center of a large galaxy dubbed 0402+379, Taylor realized he was likely observing the merging of two galaxies.

Taylor couldn’t prove it at the time, but he suspected the black holes were orbiting each other before eventually merging.

“Even though this is happening, we think, all around the universe, it’s been difficult to detect,” Taylor said.

Taylor said the black holes will merge, probably millions of years from now.

Last year’s groundbreaking research by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in Louisiana and Washington observed smaller black holes, known as stellar black holes, merging for the first time, but Taylor predicts the merging of the black holes in Bansal’s research will be even more spectacular.

“At some point, we’ll discover the coalescence of supermassive black holes,” he said. “I mean, it’s got to be a good show, given the amount of energy involved.”

The results bring to the forefront an ongoing question for astronomers: Why is it so difficult to find a pair of orbiting supermassive black holes?

Mitch Begelman, a professor at the University of Colorado’s department of astrophysical and planetary sciences, said he thinks the merging process must occur more quickly than initially believed.

” ‘Quickly’ for an astronomer,” Begelman said. “When they’re as close as these are, the final merger of those black holes will probably take millions of years.”

A false color map from the Very Large Baseline Array of the galaxy where the black holes were observed. (UNM)

Taylor agreed.

“If they hung around for billions and billions of years, we’d see lots of them out in the sky,” he said. “We had to be lucky to see this one.”

The very act of measuring the motion is an impressive display of technological achievement.

Bansal said the black holes orbit each other once every 30,000 years, so from this far away and in just over 10 years of observation, their movement appears minuscule.

Research team member and Stanford University physics professor Roger W. Romani compared it to observing a snail traveling a centimeter per second on an Earthlike planet orbiting Proxima Centauri, a star 4.2 light-years from Earth.

“I’m very impressed these researchers were able to complete these measurements,” said Lynn Cominsky, a physics and astronomy professor at Sonoma State University in California. “The real significance of this work is that it shows that supermassive black holes behave the same way as their cousins, stellar black holes.”

Bansal said the research may also give a glimpse into the future of our own galaxy.

The nearby Andromeda galaxy is on a collision course with the Milky Way.

Someday, billions of years from now, the two supermassive black holes at the center of each may perform a similar dance to the one Bansal is observing today.

The research has received huge media attention from around the globe; Bansal said it was covered by The Times of India in her native country.

Forbes, NBC and Newsweek have also reported on the story.

An online press release on the research has had 320 million hits since being posted June 29, Taylor said.

He said he believes public interest in black holes was piqued after the LIGO research came out last year.

“I’ve never had a publication get this much media attention,” Taylor said. “We’re just kind of riding the wave of interest in black holes.”

Taylor hopes to ride that wave to additional funding to continue observing and measuring the motion of the supermassive black holes and look for other similar pairs.

“Maybe now is the time,” he said.

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