In 2012, scientists detected infrared emissions from an unidentified formation named G2 that suggested a collision course that tracked the formation’s progress toward the center of the Milky Way. Originally believed to be a pure gas cloud, G2 was predicted to produce immense radiation signals as it approached Sagittarius A* (Sgr A*), the black hole at the center of our galaxy.
Scientists believe that G2, although unidentified, orbits around the massive black hole Sagittarius A* at the center of our Milky Way, photographed in this image by NASA’s Spitzer Space Telescope.
However, since G2 completed its periapse around Sgr A* around March 2014 without undergoing the predicted “tidal disruptions,” scientists have begun to debate the nature of the formation.
Based on recent observations of G2, scientists led by Andrea Ghez of the University of California, Los Angeles have posited a new theory that G2 is actually a recent binary merger of two stars surrounded by a thick shell of dust, rather than a pure gas cloud.
Ghez and her team observed G2, described as a “dusty red object,” using Keck microscopes at the W. M. Keck Observatory in Hawaii over a six-month period from March to August 2014 and collected images using near-infrared cameras.
The consistency between recent brightness measurements of G2 and those spanning the previous decade as well as the observed Keplerian motion of the formation support the idea that G2 is not a gas cloud and that itcontains a star at its center.
Since calculations of the approximate radius of this central star yielded numbers 100 times greater than a typical star, Ghez and her team theorized that G2 contained a binary merger of two stars comparable to the stars in the S-star cluster known to surround Sgr A*. This would make the mass of the central star in the formation approximately twice that of the sun. According to Ghez, such binary star mergers are promoted by the immense gravity of the black hole Sgr A*.
Despite the evidence cited in this new theory, researchers continue to disagree over the true identity of G2.
Some, like Stefan Gillessen of the Max Planck Institute for Extraterrestrial Physics in Germany, whose team originally published observations on G2, maintain that G2 is a gas cloud. Gillessen argues that G2’s “failure” to produce significant tidal disruptions can be explained by a time lapse between the production and detection of radiation. With respect to its expansion approaching Sgr A* and contraction as it moved past, Gillessen says G2 behaved exactly as would be expected of a gas cloud.
Since the identity of G2 has not been definitively determined as of yet, it remains an object of great interest to scientists, who hope that studies of G2’s interactions with Sgr A* may yield more information about both astronomical objects.
Sources:
1. Witzel, G., Ghez, A.M., Morris, M.R., Sitarski, A., Boehle, A., Naoz, S., …, Wizinowich, P. (2014, November 3). Direction of galactic center source G2 at 3.8μm during periapse passage. The Astrophysical Journal Letters. doi: 10.1088/2041-8205/796/1/L8
2. Clery, D. (2014, November 4). Astronomers identify mysterious object at heart of Milky Way. Nature. Retrieved from www.news.sciencemag.org
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