Astronomers observed a bright white dwarf, a ‘zombie star’

zombie star location

Astronomers have observed a star, a white dwarf, that survived a supernovae explosion and emerged being still brighter than before. Located 108 million light years from Earth, this white dwarf is in a spiral galaxy called NGC 1309, about three quarters the size of our Milky Way. A light year is the distance light travels in a year – 5.9 trillion miles (9.5 trillion km).

What is white dwarf: How is the star?

  • A white dwarf is the remaining core of a star that blew off a lot of its material at the end of its life cycle, as our sun is expected to do about 5 billion years from now. The white dwarf, an incredibly dense object with about the mass of the sun crammed into the size of Earth, was observed with the Hubble Space Telescope.
  • Astronomers say this white dwarf is gravitationally locked in orbit with another star – a pairing called a binary system – and with its strong gravitational pull siphoned off and incorporated a good deal of material from this unfortunate companion.
  • But for astronomers, that is where the trouble started. In doing so, the white dwarf reached a mass threshold – about 1.4 times that of the sun – that caused thermonuclear reactions in its core that made it detonate in a supernova, an event that should have killed it.
  • Curtis McCully, a senior astrodata scientist at California-based Las Cumbres Observatory, lead author of the research published this month in the Astrophysical Journal, said that they were quite surprised that the star itself had not been destroyed but “had actually survived and is brighter than before it exploded“.
  • “During the explosion, radioactive material was produced. This is what powers the brightness of the supernova. Some of this material was left over in the surviving remnant star and acted as fuel to heat the remnant”, added McCully.

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Among various types of supernovae, depending on the size and composition of the star and the power of the blast, this, which falls in the “type lax” category, is expected to helping scientists better understand about the type of supernovae.

In these, a white dwarf experiences runaway nuclear fusion of carbon and oxygen after gaining matter relatively quickly, as this one did by stealing from its companion. But the explosion does not destroy the white dwarf, leaving behind an “undead” remnant.

That’s why astronomers call these objects ‘zombie stars’. McCully said, “We have called these objects ‘zombie stars’ for this very reason. They died but not quite. Early on, many of the simulations of supernovae performed by scientists fizzled out before they were able to blow up the whole white dwarf star. It’s exciting to think that was telling us something about the actual physics of these supernovas”.

This is crucial for scientists as they to date have detected about 50 of this type of supernova, however until now, they were unable to pinpoint the surviving “zombie star” white dwarf.

Predicting the destiny of our sun as to become a white dwarf, the fate of about 97% of stars, McCully said, “At the end of a star’s life – for stars like our sun or a little bigger – the star runs out of fuel in the core and begins to collapse to a white dwarf. During this process, the outer layers of the star are puffed off into a nebula. The leftover core of the star is the white dwarf.”

But our sun cannot become a zombie star as it does not have the requisite companion star.

  • June 29, 2022
Universe & Existence