Astronomers have identified the remains of a rare type of supernova in our home galaxy for the first time. These events, known as Type Iax supernovae, occur when white dwarfs explode and may leave behind a “zombie star.”
Not all supernovae are created equal. Some occur when massive stars run out of fuel and collapse into a neutron star or black hole. Others are produced by white dwarf stars that slurp too much material off a companion star, triggering runaway nuclear fusion. The latter is known as a Type Ia supernova, and the brightness they emit is so consistent that they’ve been dubbed “standard candles” and used as yardsticks to measure distance in the cosmos.
A rare subgroup of these is what’s called Type Iax, which appear to occur under similar circumstances but throw off material at a slower speed and don’t shine as bright. Only about 30 of these are currently known and, most intriguingly, they’ve been hypothesized to leave behind an unexploded remnant nicknamed a zombie star.
And now, astronomers may have discovered the smoking gun of one of these Type Iax supernovae in the Milky Way, for the first time. The object in question is named Sagittarius A East (Sgr A East), and located close to the center of the galaxy near the similarly-named supermassive black hole, Sagittarius A*.
Sgr A East has appeared as a cloud-like shape on images of the region for decades, with astronomers mostly assuming it to be a run-of-the-mill supernova remnant, or perhaps a Type Ia. But for the new study, researchers used the Chandra X-Ray Observatory to watch the object for 35 days, and found that it’s probably a Type Iax.
“While we’ve found Type Iax supernovae in other galaxies, we haven’t identified evidence for one in the Milky Way until now,” says Ping Zhou, lead author of the study. “This discovery is important for getting a handle of the myriad ways white dwarfs explode.”
The team came to this conclusion by studying Sgr A East’s X-ray spectrum, which can reveal the fingerprints of elements produced in the explosion, and in what amounts they occur. From this, the researchers came to the conclusion that the blast was weaker than most, in line with a Type Iax supernova.
“This supernova remnant is in the background of many Chandra images of our galaxy’s supermassive black hole taken over the last 20 years,” says Zhiyuan Li, an author of the study. “We finally may have worked out what this object is and how it came to be.”
If its identity is confirmed, the team says this would be the closest known Type Iax supernova to Earth – and possibly, the nearest zombie star, too.
The research was published in the Astrophysical Journal. The work is described in the video below.
Source: NASA