A white dwarf star called SDSS J124043.01 + 671034.68 (SDSS J1240 + 6710) travels at 900,000 km / h (559,234 mph) through our Milky Way. It also has a particularly low mass for a white dwarf, only 40% of the mass of our Sun, which would be consistent with the loss of mass of a partial supernova. According to new research, SDSS J1240 + 6710 likely belonged to a binary system that survived an alleged thermonuclear supernova event, which sent him and his partner to fly through the Milky Way in opposite directions.
Artist’s impression of a thermonuclear supernova: The material ejected by the supernova will initially expand very rapidly, but then gradually decrease, forming an intricate giant bubble of hot, glowing gas; finally, the charred remains of the exploded white dwarf will overcome these gaseous layers and accelerate their journey through our Galaxy, the Milky Way. Image credit: Mark Garlick / University of Warwick.
White dwarfs are the remaining cores of red giants after these huge stars have died and shed their outer layers, cooling down over the course of billions of years.
Most white dwarfs have atmospheres made up almost entirely of hydrogen or helium, with occasional evidence of carbon or oxygen extracted from the star’s core.
SDSS J1240 + 6710, which was discovered in 2015, is 1,432 light-years away from us in the Draco constellation.
Also known as WD 1238 + 674 and LSPM J1240 + 6710, the star was found to have an oxygen-dominated atmosphere with significant traces of neon, magnesium, and silicon.
“This star is unique because it has all the key characteristics of a white dwarf, but it has very high speed and unusual abundances that are meaningless when combined with its low mass,” said Professor Boris Gaensicke, lead author at the University of Warwick. study.
Using the cosmic-origin spectrograph aboard the NASA / ESA Hubble Space Telescope, Professor Gaensicke and his colleagues identified carbon, sodium, and aluminum in the atmosphere from SDSS J1240 + 6710, all of which occur in early thermonuclear reactions from a supernova.
However, there is a clear absence of what is known as the “iron group” of elements, iron, nickel, chromium, and manganese.
These heavier elements are normally cooked from the lighter ones and constitute the defining characteristics of thermonuclear supernovae.
The lack of elements of the iron group in SDSSJ1240 + 6710 suggests that the star only went through a partial supernova before the nuclear burn was extinguished.
“The white dwarf has a chemical composition that is the fingerprint of nuclear combustion, a low mass, and a very high rate: all of these facts imply that it must come from some kind of nearby binary system and must have undergone thermonuclear ignition,” Professor Gaensicke said.
“It would have been a type of supernova, but a type that we haven’t seen before.”
The authors theorize that the supernova disrupted the white dwarf’s orbit with its companion star when it abruptly ejected a large proportion of its mass.
Both stars would have been driven in opposite directions to their orbital speeds in a sort of slingshot maneuver. That would explain the high speed of the star.
“If it was a narrow binary and it underwent thermonuclear ignition, expelling much of its mass, you have the conditions to produce a low-mass white dwarf and make it fly at orbital speed,” said Professor Gaensicke.
The best studied thermonuclear supernovae are type Ia. But there is increasing evidence that thermonuclear supernovae can occur under very different conditions.
SDSSJ1240 + 6710 may be the survivor of a type of supernova that has not yet been caught on the spot.
Without the radioactive nickel that powers the long-lasting glow of Type Ia supernovae, the blast that sent SDSS1240 + 6710 at full speed over our galaxy would have been a brief flash of light that would have been difficult to detect.
“The study of thermonuclear supernovae is a huge field and there is a great deal of observational effort to find supernovae in other galaxies,” said Professor Gaensicke.
“The difficulty is that you see the star when it explodes, but it is very difficult to know the properties of the star before it explodes.”
“The fact that such a low-mass white dwarf went through burning carbon is a testament to the effects of interactive binary evolution and its effect on the chemical evolution of the Universe,” said lead author Professor SO Kepler, astronomer. from the United States Federal University. Rio Grande do Sul.
“Once again, the synergy between highly accurate Gaia astrometry and spectroscopic analysis has helped to restrict the surprising properties of a single white dwarf, which probably formed in a thermonuclear supernova and was ejected at high speed as a result of the explosion. “said co-author Dr. Roberto Raddi, astronomer at the Universitat Politècnica de Catalunya.
The team’s article was published in the Monthly notices from the Royal Astronomical Society.
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Boris T. Gänsicke et al. 2020. SDSS J124043.01 + 671034.68: The partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition? MNRAS 496 (4): 4079-4086; doi: 10.1093 / mnras / staa1761
This article is based on a press release provided by the University of Warwick.
