Astronomers have discovered a white dwarf that narrowly escaped its own thermonuclear explosion, raising questions about how and why these stars create supernovae.
a white dwarf is the evolutionary end point of the sunlike a star. After this star swells to become red giantthen runs out of fuel required for nuclear fusion reactions, the star ejects its outer layers to form a planetary nebula, or a shell of circulating gas. When the nebula expands and dissipates, it leaves behind the inert core of the star, which is what we call a white dwarf.
white dwarfs size a land, but it has a mass equal to the mass of the star. As such, they are dense objects with a gravitational pull strong enough to pull material from any nearby companion stars. This material flows onto the white dwarf, and once enough material has accumulated, it explodes in a thermonuclear explosion that usually destroys the star in what scientists call Type I. supernovae.
Or so we thought.
In 2012, when astronomers saw a supernova called 2012Z exploding in the face-to-face spiral galaxy NGC 1309, which is about 120 million light years Far from Earth in the constellation Eridanus, the Hubble Space Telescope He was fast at the scene. Hubble imaged NGC 1309 several times in the years leading up to the supernova, and astronomers were able to identify the progenitor star system that exploded, finding that it contained a white dwarf that snatched material from an ancient helium-rich star, possibly red giant.
These observations marked the first time that scientists had imaged an ancestor of a Type Ia supernova. However, something seemed to be wrong with the Hubble data. Not only did the images show that the ancestor somehow survived the explosion, but the white dwarf was also somehow brighter than before.
Curtis McCauley, an astrophysicist at the Las Cumbres Observatory in California, said in a statement statement. “That was a real mystery.”
Astronomers have identified what they suspect are failed Type Ia supernovae leaving behind the remains of “zombie” stars – a phenomenon called Type Iax supernovas. One of the most notable of these supernovae was SN 2008ha, which exploded in the galaxy UGC 12682 about 69 million light-years from Earth in the constellation UGC 12682. winged horse. However, SN 2012Z is the first time astronomers have confirmed the survival of the supernova, based on images taken before and after the supernova.
McCauley and colleagues, having studied SN 2012Z, have a partial theory about what happened. The researchers suggest that the thermonuclear explosion wasn’t powerful enough to blow the white dwarf away completely, and that much of the debris fell back onto the star, inflating the white dwarf into what astronomers call a “bound remnant.” Over time, scientists expect the star to return to its original, calm state.
The surviving white dwarf may be brighter than before due to light from a number of sources, including the glowing remnant itself, and its shockingly hot companion. star that received the brunt of the explosion, the radioactive decay of materials that escaped into space during the explosion.
The light of a Type Ia supernova is usually triggered by the radioactive decay of cobalt-56 and -57 isotopes in matter emitted into space. (Isotopes are varieties of an atom that have the same number of protons and electrons but different numbers of neutrons.) These isotopes have half-lives of 77 and 271 days, respectively, so after a few years, most of the cobalt has decayed and the supernova light is drastically fading out.
However, SN 2012Z decays much more slowly, so if radioactive decay is the primary source of light, it must be an isotope with a much longer half-life. McCauley’s team suggests iron-55, which has a half-life of 2.7 years.
Why SN 2012Z underwent this failed supernova, rather than destroying itself in a typical Type Ia, remains a mystery.
“The implications for Type Ia supernovae are profound,” McCauley said. “We’ve found that at least a supernova can grow to its limit and explode. However, eruptions are weak, at least some of the time. Now we need to understand what makes a supernova fail to become a Type Iax, and what makes it successful as a Type Ia “.
Type Ia supernovae have a standard change in their brightness over time – what astronomers call the light curve – which makes determining the distance between them much easier. As such, they have become crucial to studies cosmic expansion And the dark energy. By better understanding how it explodes, astronomers will be able to measure the expansion of Universe And the power of dark energy for greater accuracy than before.
The results were published on February 1 at Astrophysical Journal.
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