'Needle-in-a-haystack' search finds possible phantom-like black hole roaming the Milky Way

Of course you know about black holes. But did you know there may be millions of them drifting like ghosts throughout our galaxy?

Since black holes are invisible, they are identified by statistical means or by seeing a black hole’s effects on another star or a second black hole. But moving black holes – ghostly remains of collapsed stars – have been impossibly elusive.

Astronomers estimate there may be 100 million black holes roaming through our galaxy, based on the Milky Way's 100 billion stars (some of which eventually collapse and become black holes). Two astronomical research teams have announced they used Hubble Space Telescope data to find, for the first time, what appears to be a black hole moving through our galaxy.

What sends a black hole into motion? When a star explodes in a supernova, gravity crushes its core and creates a black hole. However, an asymmetrical explosion can send the black hole "careening through our galaxy like a blasted cannonball," according to a description of the new findings on NASA's Hubble Site.

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An illustration of a close-up look at a black hole drifting through the Milky Way galaxy.
An illustration of a close-up look at a black hole drifting through the Milky Way galaxy.

Researchers were alerted to the possible black hole after telescopes watching for changes in the brightness of stars captured some anomalies about 5,000 light-years away in the Carina-Sagittarius spiral arm of our galaxy, NASA said.

The two research teams – one based at the Space Telescope Science Institute in Baltimore, Maryland, the other at the University of California, Berkeley – studied six years of the Hubble telescope's data to investigate more closely, using a technique called gravitational microlensing.

Since a black hole warps the surrounding space, it bends and amplifies the light of any star in its background. Hubble's precise recordings helped researchers measure how the light from a background star 19,000 light-years away had been changed by the potential black hole passing in front of it. It also helped them determine the mass, distance, and velocity of the black hole, NASA said.

The isolated black hole is traveling at an estimated 100,000 mph – fast enough to travel from Earth to the Moon in less than three hours, The Space Telescope Science Institute research team said.

Hubble's data included 270 days during which the background star's light was amplified as the black hole passed in front of it. Hubble also revealed how the star's image was deflected by a milliarcsecond, comparable to the diameter of a 25-cent coin in Los Angeles viewed from New York City, NASA said.

Another nearby unrelated star made the measurements difficult, astronomer Kailash Sahu, who led The Space Telescope Science Institute team, said in a statement on the NASA site.

"So it's like trying to measure the tiny motion of a firefly next to a bright light bulb," he said. "We had to meticulously subtract the light from the nearby bright star to precisely measure the deflection of the faint source."

His team estimated the black hole to weigh the equivalent of seven of our suns. Their research, posted on the arXiv archive of scientific research, has been accepted for publication in The Astrophysical Journal, Sahu told USA TODAY.

But there's some disagreement on how big the black hole is – or even if it is a black hole. The University of California, Berkeley researchers estimate the mass of the object at between 1.6 and 4.4 times that of our sun, NASA said. At the lower end of that range, the object could actually be a neutron star, researchers say.

That team's research, also posted on arXiv, has been accepted for publication in The Astrophysical Journal Letters, according to Science Daily.

Like black holes, neutron stars are also formed when a star collapses. However, these stellar objects stop short of becoming black holes, from which gravity is so strong light cannot escape.

"As much as we would like to say it is definitely a black hole, we must report all allowed solutions. This includes both lower-mass black holes and possibly even a neutron star," Jessica Lu, a University of California, Berkeley associate professor of astronomy, said in a statement on NASA's site and the UC Berkeley site.

Black holes: Two collided billions of years ago. The spectacle is just beginning to reach Earth.

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Both research teams have been analyzing additional Hubble data – and this, along with future discoveries – will help scientists better understand our galaxy and possibly lead to a definitive finding on this particular object.

For now, researchers can be congratulated for their find, which NASA deemed the equivalent of a galactic "needle-in-a-haystack search."

Casey Lam, a graduate student who led the UC Berkeley team, said on the NASA site, "Whatever it is, the object is the first dark stellar remnant discovered wandering through the galaxy unaccompanied by another star."

Follow Mike Snider on Twitter: @mikesnider.

This article originally appeared on USA TODAY: NASA: Hubble Space Telescope data discovers roaming black hole