A white dwarf star has been spotted hurtling through the Milky Way at 560,000 miles per hour thanks to a thermonuclear blast from a ‘partial supernova’, study found.
Astronomers from the University of Warwick used observations from the Hubble Space Telescope to find out what sent the white dwarf on its journey.
The white dwarf has an ‘unusual atmospheric composition’ that suggests it was actually a binary star that was able to survive a supernova explosion and was flung out of the system with its pair going in the opposite direction.
This opens up the possibility of many more survivors of supernovae travelling undiscovered through the Milky Way, according to the Warwick team.
White dwarfs are the remaining cores of red giants after these huge stars have died and shed their outer layers, cooling over the course of billions of years.
This star, called SDSS J1240+6710, was discovered in 2015 and seemed to contain neither hydrogen nor helium when it was first spotted in the sky.
The white dwarf has an ‘unusual atmospheric composition’ that suggests it was actually a binary star that was able to survive a supernova explosion and was flung out of the system with its pair going in the opposite direction
The majority of white dwarfs have atmospheres composed almost entirely of hydrogen or helium, with occasional evidence of carbon or oxygen from the core.
SDSS J1240+6710 is composed of a mix of oxygen, neon, magnesium and silicon.
Using the Hubble Space Telescope, the scientists also identified carbon, sodium, and aluminium in the star’s atmosphere, all of which are produced in the first thermonuclear reactions of a supernova.
However, there is a clear absence of what is known as the ‘iron group’ of elements, iron, nickel, chromium and manganese – defining features of a supernova.
These heavier elements are normally cooked up from the lighter ones and the lack of iron group elements suggests that the star only went through a partial supernova before the nuclear burning died out.
Astronomers were able to measure the white dwarf’s velocity and found that it is travelling at 559,234 miles per hour.
It also has a particularly low mass for a white dwarf – only 40 per cent the mass of our Sun – which would be consistent with the loss of mass from a partial supernova.
Lead author Professor Boris Gaensicke from the Department of Physics at the University of Warwick said the star was particularly unique.
‘It has all the key features of a white dwarf but it has this very high velocity and unusual abundances that make no sense when combined with its low mass.
‘It has a chemical composition which is the fingerprint of nuclear burning, a low mass and a very high velocity,’ he explained.
Gaensicke said all of these facts imply that it must have come from some kind of close binary system and it must have undergone thermonuclear ignition.
‘It would have been a type of supernova, but of a kind that that we haven’t seen before,’ he explained.
The scientists theorise that the supernova disrupted the white dwarf’s orbit with its partner star when it very abruptly ejected a large proportion of its mass.
Both stars would have been carried off in opposite directions at their orbital velocities in a kind of slingshot manoeuvre.
That would account for the star’s high velocity, the Warwick astronomers explained.
‘If it was a tight binary and it underwent thermonuclear ignition, ejecting quite a lot of its mass, you have the conditions to produce a low mass white dwarf and have it fly away with its orbital velocity,’ Professor Gaensicke said.
The best studied thermonuclear supernovae are the ‘Type Ia’, which led to the discovery of dark energy, and are now used to map structure of the Universe.
There is growing evidence that thermonuclear supernovae can happen under very different conditions to the Type 1a versions widely studied.
The SDSSJ1240+6710 white dwarf may be the survivor of a type of supernova that hasn’t yet been ‘caught in the act’ of explosion, the team said.
Astronomers from the University of Warwick used observations from the Hubble Space Telescope to find out what sent the white dwarf on its journey
Without the radioactive nickel that powers the long-lasting afterglow of the Type Ia supernovae, the explosion that sent SDSS1240+6710 hurtling across our Galaxy would have been a brief flash of light that would have been difficult to discover.
‘The study of thermonuclear supernovae is a huge field and there’s a vast amount of observational effort into finding supernovae in other galaxies,’ said Gaensicke.
‘The difficulty is that you see the star when it explodes but it’s very difficult to know the properties of the star before it exploded.’
The team have discovered that there are different types of white dwarf that can survive a supernovae under different conditions and with different compositions, masses and velocities.
Gaensicke said this means they can figure out what type of supernova they have undergone to become a white dwarf.
‘There is clearly a whole zoo out there. Studying the survivors of supernovae in our Milky Way will help us to understand the myriads of supernovae that we see going off in other galaxies,’ he said.
Professor S.O. Kepler of Universidade Federal do Rio Grande do Sul, Brazil, and who originally discovered this star, said it was an unusual discovery.
‘The fact that such a low mass white dwarf went through carbon burning is a testimony of the effects of interacting binary evolution and its effect on the chemical evolution of the Universe,’ he said.
The findings were published in Monthly Notices of the Royal Astronomical Society.
SUPERNOVAE OCCUR WHEN A GIANT STAR EXPLODES
A supernova occurs when a star explodes, shooting debris and particles into space.
A supernova burns for only a short period of time, but it can tell scientists a lot about how the universe began.
One kind of supernova has shown scientists that we live in an expanding universe, one that is growing at an ever increasing rate.
Scientists have also determined that supernovas play a key role in distributing elements throughout the universe.
In 1987, astronomers spotted a ‘titanic supernova’ in a nearby galaxy blazing with the power of over 100 million suns (pictured)
There are two known types of supernova.
The first type occurs in binary star systems when one of the two stars, a carbon-oxygen white dwarf, steals matter from its companion star.
Eventually, the white dwarf accumulates too much matter, causing the star to explode, resulting in a supernova.
The second type of supernova occurs at the end of a single star’s lifetime.
As the star runs out of nuclear fuel, some of its mass flows into its core.
Eventually, the core is so heavy it can’t stand its own gravitational force and the core collapses, resulting in another giant explosion.
Many elements found on Earth are made in the core of stars and these elements travel on to form new stars, planets and everything else in the universe.