Image credit: Sephirohq (CC BY SA 3.0)
Supernovae, by their nature, often don’t leave many stars for astronomers to examine later. Many of these titanic explosions result in the formation of a black hole or a neutron star. For many years, scientists believed that most supernovae resulted in one of three results: black hole, neutron star, or nothing at all. Now we have found a new star that is neither of those things and seems to be the survivor of a partial supernova. Such stars have been called zombie stars since a candidate for such an event was identified in 2012, but researchers have found a considerably closer candidate in our own Milky Way.
Our proposed supernova remnant has the catchy name of SDSS J1240 + 6710. It is currently accelerating through the Milky Way in the opposite direction to standard galactic rotation at 560,000 miles per hour, or 0.000835 the speed of light. Before making fun of speed, keep in mind that we are still talking about a star, neither of which is particularly light.
What distinguishes this star?
Scientists have found enough white dwarfs in the universe to get a pretty good idea of what their stellar atmospheres are like. Hydrogen and helium dominate the atmospheric composition of these stars, which is why J1240 + 6710 is so strange. When the star was discovered in 2015, astronomers found an atmosphere made up of oxygen, neon, magnesium, and silicon. When reexamined with specialized detectors in the far ultraviolet range, they found a mixture of carbon, sodium, and aluminum. Oxygen dominates the atmosphere, but all other elements are present at least in small amounts. This is completely different from what we expect to find in the star atmosphere of a white dwarf.
Revealingly, there are no elements of the iron group, either. We should see chrome, iron, manganese, and nickel. All are missing When a star becomes a supernova, the heaviest elements are formed from lighter elements, but not here.
Image credit: Rursus (CC BY-SA 2.5)
The image above shows the estimated core layers of a star about to become a supernova. The elements we have found, such as carbon, neon, oxygen, and silicon, are the outermost layers of the star, which surround an iron core. The fact that we see every layer of elements represented in this star’s atmosphere except For the iron group, the metals suggest that this star is a remnant of a partial supernova.
In this case, the thermal leak that normally initiates a Type Ia supernova was hampered by some mechanism or failure midway. J1240 + 6710 is also a low-mass white dwarf, which conforms to this theory. The failed supernova ejected enough material from the star to throw it into the broader galaxy in a trajectory opposite to the rest of the Milky Way, but it did not completely destroy the star itself. This research was published in the Royal Astronomical Society and you can read the full report here.
The characteristic image is a white dwarf created by Sephirohq and uploaded to Wikipedia. The photo is (CC BY 3.0).
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