November 04, 2014
from EarthSky Website

Spanish version
 

 

 

 

Astronomers watched in fascination

as an object called G2 appeared

to edge closer to our Milky Way's central black hole.

But G2 survived!
 

 

 

An image from W. M. Keck Observatory near infrared data shows that G2 survived its closest approach to the black hole in northern summer 2014. The green circle just to its right depicts the location of the invisible supermassive black hole.

Image via Keck Observatory

 

 

In 2011, astronomers said they'd discovered a cloud of gas - with several times Earth's mass - accelerating fast towards the supermassive black hole at the center of our Milky Way.

 

The cloud appeared to be undergoing spaghettification - sometimes called the noodle effect - stretching and elongating as it neared the black hole. It was thought at first the cloud - which came to be called G2 - would meet a fiery end as it passed into the Milky Way's black hole as early as 2013.

 

It did not, but astronomers now say it passed closest to the hole in northern summer of 2014. Unexpectedly, however, our galaxy's black hole did not swallow it. Instead, G2 survived!

 

This week (November 3, 2014), UCLA astronomers published a new paper (Detection of Galactic Center Source G2 at 3.8 Microns during Periapse Passage) in the journal Astrophysical Journal Letters offering a new explanation as to what G2 is and how it survived its black hole passage.

 

Andrea Ghez, UCLA professor of physics and astronomy, said in a press release:

  • G2 survived and continues happily on its orbit; a gas cloud would not do that

  • G2 was completely unaffected by the black hole. There were no fireworks

Ghez' team now suggests that G2 is a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star. This merger may have been cloaked in gas and dust, and choreographed by the object's proximity to the black hole's powerful gravitational field.

 

Ghez said:

G2 is not alone. We're seeing a new class of stars near the black hole, and as a consequence of the black hole.

Ghez noted that massive stars in our galaxy primarily come in pairs.

 

When the two stars merge into one, the star expands for more than one million years, Ghez said,

…before it settles back down.

 

This may be happening more than we thought; the stars at the center of the galaxy are massive and mostly binaries. It's possible that many of the stars we've been watching and not understanding may be the end product of a merger that are calm now.

G2, on the other hand, would be in its expansive stage now.

 

It appears to have an unusual, 300-year elliptical orbit around the black hole.

 

 

Telescopes from Hawaii's W.M. Keck Observatory use a powerful technology called adaptive optics, which enabled UCLA astronomers to study G2 and suggest it is a pair of binary stars that merged together, cloaked in gas and dust.

Image via Keck Observatory

 

 

Bottom line:

 

Astronomers watched in fascination as an object called G2 - apparently a gas cloud - appeared to edge closer and closer to our Milky Way's central black hole.

 

But G2 survived!

 

Now, instead of a gas cloud, astronomers believe G2 is a binary star system, that is, two that had been orbiting the black hole in tandem and merged together into an extremely large star.

 

 

 

 

 

 

 

 

 

 

 


Mysterious G2 Cloud

...Near Black Hole Identified
November 3, 2014
from KeckObservatory Website

 

 

Keck Observatory

is a private 501(c) 3 non-profit organization

and a scientific partnership of

the California Institute of Technology,

the University of California

and NASA.


 

 

Credit: Andrea Ghez, Gunther Witzel/UCLA Galactic Center Group/W. M. Keck Observatory

An image from W. M. Keck Observatory near infrared data shows that G2 survived its closest approach to the black hole and continues happily on its orbit.

 

The green circle just to its right depicts the location of the invisible supermassive black hole.
 

 

Credit: Ethan Tweedie Photography

Telescopes from Hawaii's W.M. Keck Observatory use a powerful technology called adaptive optics, which enabled UCLA astronomers to discover that G2 is a pair of binary stars that merged together, cloaked in gas and dust.


 

MAUNA KEA, Hawaii

 

The mystery about a thin, bizarre object in the center of the Milky Way headed toward our galaxy's enormous black hole has been solved by UCLA astronomers using the W.M. Keck Observatory, home of the two largest telescopes on Earth.

 

The scientists studied the object, known as G2, during its closest approach to the black hole this summer, and found the black hole did not dine on it.

 

The research is published today in the journal Astrophysical Journal Letters (Detection of Galactic Center Source G2 at 3.8 Microns during Periapse Passage).

 

While some scientists believed the object was a cloud of hydrogen gas that would be torn apart in a fiery show, Andrea Ghez and her team proved it was much more interesting.

"G2 survived and continues happily on its orbit; a gas cloud would not do that," said Andrea Ghez, UCLA professor of physics and astronomy who holds the Lauren B. Leichtman and Arthur E. Levine Chair in Astrophysics, and directs the UCLA Galactic Center Group.

 

"G2 was completely unaffected by the black hole; no fireworks."

Instead, the team has demonstrated it is a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star, cloaked in gas and dust, and choreographed by the black hole's powerful gravitational field.

"G2 is not alone," said Ghez, who uses Keck Observatory to study thousands of stars in the neighborhood of the supermassive black hole.

 

"We're seeing a new class of stars near the black hole, and as a consequence of the black hole."

Ghez and her colleagues - who include lead author Gunther Witzel, a UCLA postdoctoral scholar in Ghez's research group, and Mark Morris, a UCLA professor of physics and astronomy - studied the event with both of the 10-meter telescopes at Keck Observatory.

 

Keck Observatory employs a powerful technology called adaptive optics, which Ghez helped to pioneer, to correct the distorting effects of the Earth's atmosphere in real time, and to reveal the region of space around the black hole.

 

With adaptive optics, Ghez and her colleagues have revealed many surprises about the environments surrounding supermassive black holes, discovering, for example, young stars where none were expected and seeing a lack of old stars where many were anticipated.

"The Keck Observatory has been the leader in adaptive optics for more than a decade and has enabled us to achieve tremendous progress in correcting the distorting effects of the Earth's atmosphere using high–angular resolution imaging techniques," Ghez said.

The researchers wouldn't have been able to arrive at their conclusions without the Keck's advanced technology.

"It is a result that in its precision was possible only with these incredible tools, the Keck Observatory's 10-meter telescopes," Witzel said.

 

"We are seeing phenomena about black holes that you can't watch anywhere else in the universe," Ghez added. "We are starting to understand the physics of black holes in a way that has never been possible before, and is possible only at the center of the galaxy."

Massive stars in our galaxy, she noted, primarily come in pairs.

 

When the two stars merge into one, the star expands for more than one million years, "before it settles back down," Ghez said.

"This may be happening more than we thought; the stars at the center of the galaxy are massive and mostly binaries. It's possible that many of the stars we've been watching and not understanding may be the end product of a merger that are calm now."

G2, in that explosive stage now, has been an object of fascination.

"Its closest approach to the black hole was one of the most watched events in astronomy in my career," Ghez said.

G2 makes an unusual, 300-year elliptical orbit around the black hole and Ghez's group calculated its closest approach occurred this summer - later than other astronomers believed - and they were in place at Keck Observatory to gather the data.

 

Black holes, which form out of the collapse of matter, have such high density that nothing can escape their gravitational pull, not even light. They cannot be seen directly, but their influence on nearby stars is visible and provides a signature, said Ghez, a 2008 MacArthur Fellow.

 

The W.M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth.

 

The two, 10-meter optical/infrared telescopes near the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectographs and world-leading laser guide star adaptive optics systems.

 

NIRC2 (the Near-Infrared Camera, second generation) works in combination with the Keck II adaptive optics system to obtain very sharp images at near-infrared wavelengths, achieving spatial resolutions comparable to or better than those achieved by the Hubble Space Telescope at optical wavelengths.

 

NIRC2 is probably best known for helping to provide definitive proof of a central massive black hole at the center of our galaxy.

 

Astronomers also use NIRC2 to map surface features of solar system bodies, detect planets orbiting other stars, and study detailed morphology of distant galaxies.