Canadian and US astronomers have located what is thought to be the closest neutron star ever seen. The exotic object, nicknamed Calvera after the villain in the movie “The Magnificent Seven”, is located in the constellation Ursa Minor, somewhere between 250 and 1,000 light-years away. It’s a member of a rare group of isolated neutron stars – they lack binary companions – and could be just the tip of the iceberg.
The discovering astronomers pored over a gigantic catalog of 18,000 X-ray sources captured by the German-American ROSAT satellite, which was operational between 1990 and 1999. They compared these X-ray sources to objects visible other wavelengths of light, such as infrared, visible light, and radio waves. One object, 1RXS J141256.0+792204, stood out as being visible only in X-rays.
Then they targeted the object with NASA’s Swift satellite, and performed more detailed observations. Swift was able to find the source, and confirmed that it was putting out as much X-ray energy today as had been captured by ROSAT. Then they pointed one of the most powerful telescopes on Earth, the 8.1 Gemini North Telescope in Hawaii, and couldn’t find a single optical light object down to the faintest magnitudes. It was only shining in X-rays.
According to the researchers, there are no widely accepted alternate theories for objects like Calvera, which are bright in X-rays, but faint in visible light. Either it’s an unusual example of a neutron star, or it might be a completely new kind of object. Another mystery: it’s high above the plane of the Milky Way Galaxy. It must have formed in the plane, but then somehow migrated up to its current position.
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With the discovery of Calvera, astronomers think there could be many objects like this. It’s close enough that astronomers will be able to perform detailed observations with many instruments. It should yield interesting results for years to come.
Original Source: PSU News Release