Hubble telescope discovers the trick to weighing a solitary black hole

Earlier this yearastronomers have used microlens and the Hubble Space Telescope to detect, for the first time, a rogue black hole located about 5,000 light-years from Earth. Now, with more precise measurements, they were able to determine the approximate mass of this hard-to-detect object. However, the surprisingly low mass means there’s a chance this object isn’t actually a black hole.

The newly detected wandering object is about 5,000 light-years away, in the Carina-Sagittarius spiral arm of our galaxy. Two major international teams have used Hubble data in their investigations to learn more about the object, OGLE-2011-BLG-0462/MOA-2011-BLG-191 or OB110462 for short). A team was led by Kailash Sahu from the Space Telescope Science Institute in Baltimore, which led the team in the original discovery of the black hole. The second team was led by Casey Lam from the University of California, Berkeley. And while the results of the two teams differ slightly, both suggest the presence of a relatively compact object.

The star-filled sky in this NASA/ESA Hubble Space Telescope photo is in the direction of the galactic center. Starlight is monitored to see if a change in their apparent brightness is caused by a foreground object drifting past them. The intruder’s warping of space would momentarily lighten the appearance of a background star, an effect called gravitational lensing. One of these events is illustrated in the four close-ups below. The arrow points to a star that has momentarily brightened, as first captured by Hubble in August 2011.NASA, ESA, K. Sahu (STScI), J. DePasquale (STScI)

The amount of deflection due to the object’s intense space warping allowed Sahu’s team to estimate that it weighs seven solar masses. Lam’s team reports a slightly lower mass range, meaning the object could be either a neutron star or a black hole. They estimate that the mass of the invisible compact object is between 1.6 and 4.4 times that of the Sun. At the upper end of this range, the object would be a black hole; at the lower end it would be a neutron star.

“While we’d like to say this is definitely a black hole, we need to flag all allowed solutions,” said Jessica Lu of the Berkeley team. ‚ÄúThis includes both lower mass black holes and possibly even a neutron star. Either way, the object is the first dark stellar remnant discovered wandering the galaxy, unaccompanied by another star.

However, there are other clues and features of this object that tip the data towards a black hole.

The history of this object begins in 2011 when Hubble data indicated a brightening of the star. This was determined to be due to a prominent black hole drifting past the star, along our line of sight. The star brightened and then dimmed for several months to regain its normal luminosity as the black hole passed. Because a black hole neither emits nor reflects light, it cannot be observed directly. But its unique fingerprint on the fabric of space can be measured through these microlensing events.

Dozens of astronomers from Sahu’s team have now been working for more than six years to study this object. And while astronomers have used gravitational microlens for about 30,000 events to date – studying objects such as stars and exoplanets – the signature of a black hole stands out as unique among other microlensing events.

The team said the very intense gravity of the black hole will extend the duration of the lensing event to more than 200 days. Additionally, if the intervening object were a foreground star instead, this would cause a transient color change in the starlight as measured because the foreground and background starlight would be momentarily mixed together . But no color change was seen by observing this object. That is why Sahu’s team published their paper earlier this year, claiming to have found a rogue black hole.

The existence of stellar-mass black holes has been known since the early 1970s. And so far, all black hole masses have been inferred statistically or by interactions in binary systems or in the cores of galaxies. Since stellar-mass black holes are usually found with companion stars, this new object is very unusual.

It’s been estimated that 100 million black holes roam among the stars in our galaxy, the Milky Way, and this is potentially the first time an isolated black hole has actually been discovered. If this is confirmed as the discovery of a wandering black hole, then astronomers could estimate that the closest isolated stellar-mass black hole to Earth could be as close as 80 light-years away. For reference, the closest star to our solar system, Proxima Centauri, is just over 4 light years away.

“Detections of isolated black holes will provide new information about the population of these objects in the Milky Way,” Sahu said. He expects what astronomers have learned in these observations will allow them to discover more free-roaming black holes inside our galaxy.

But even with the use of the incredible tool called a microlens, it would be a needle in a haystack search. Astronomers also predict that only one microlensing event in a few hundred is caused by isolated black holes.

“The astrometric microlens is conceptually simple but very difficult to observe,” Sahu said. “Furthermore, microlensing is the only technique available to identify isolated black holes.”

That’s why the two teams – each with dozens of astronomers – will continue to study and monitor this object, hoping for more data and more microlensing events.

This article was originally published on Universe today by Nancy Atkinson. Read it original article here.

#Hubble #telescope #discovers #trick #weighing #solitary #black #hole

Leave a Comment

Your email address will not be published. Required fields are marked *