An international team of researchers analyzing decades of observations from many facilities, including the W.M. Keck Observatory on Maunakea and the Pan-STARRS1 telescope on Haleakala, as well as NASA’s Swift satellite, has discovered an unusual source of light in a galaxy some 90 million light-years away. The team was led by Michael Koss, who was a postdoctoral fellow at the Institute for Astronomy at the University of Hawaiʻi at Mānoa during most of the time the study was ongoing.
The object’s curious properties make it a good match for a supermassive black hole ejected from its home galaxy after merging with another giant black hole. But astronomers can’t yet rule out an alternative possibility. The source, called SDSS1133, may be the remnant of a massive star that underwent a record period of eruptions before destroying itself in a supernova explosion.
“With the data we have in hand, we can’t yet distinguish between these two scenarios,” said Koss, now an astronomer at ETH Zurich, the Swiss Federal Institute of Technology. “One exciting discovery made with NASA’s Swift is that the brightness of SDSS1133 hasn’t changed in ultraviolet light for a decade, which is not something typically seen in a young supernova remnant.”
In a study published in the November 21 edition of Monthly Notices of the Royal Astronomical Society, Koss and his colleagues report that the source has brightened significantly during the past six months, a trend that, if maintained, would bolster the black hole interpretation.
To analyze the object in greater detail, the team is planning ultraviolet observations with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope in October 2015. “We found in the Pan-STARRS1 imaging that SDSS1133 is getting significantly brighter over the last 6 months and that bolstered our case to study SDSS1133 now with HST,” said Yanxia Li a UH Mānoa graduate student involved in the analysis of the Pan-STARRS1 imaging in the study.
Whatever SDSS1133 is, it’s persistent. The team was able to detect it in astronomical surveys dating back more than 60 years.
“We suspect we’re seeing the aftermath of a merger of two small galaxies and their central black holes,” said co-author Laura Blecha, an Einstein Fellow in the University of Maryland’s Department of Astronomy and a leading theorist in simulating recoils, or “kicks,” in merging black holes. “Astronomers searching for recoiling black holes have been unable to confirm a detection, so finding even one of these sources would be a major discovery.”
—For the full story, read the UH Mānoa news release.