White Dwarf “Close” to Exploding as Supernova

Article written: 3 Sep , 2009
Updated: 24 Dec , 2015
by

ESA’s XMM-Newton orbiting X-ray telescope has uncovered the first close-up of a white dwarf star that could explode into a type Ia supernova within a few million years. That’s relatively soon in cosmic time frames, and although this white dwarf that is orbiting its companion star HD 49798, is far enough away to pose no danger to Earth, it is close enough to become an extraordinarily spectacular celestial sight. Calculations suggest that it will blaze initially with the intensity of the full Moon and be so bright that it will be seen in the daytime sky with the naked eye. But don’t worry, it will be awhile!

Astronomers have been on the trail of this mysterious object since 1997, when they discovered that something was giving off X-rays near the bright star HD 49798. Now, thanks to XMM-Newton’s superior sensitivity, the mysterious object has been tracked along its orbit. The observation has shown it to be a white dwarf, the dead heart of a star, shining X-rays into space.

Sandro Mereghetti, INAF–IASF Milano, Italy, and collaborators also discovered that this is no ordinary white dwarf. They measured its mass and found it to be more than twice what they were expecting. Most white dwarfs pack 0.6 solar masses into an object the size of Earth.

This particular white dwarf contains at least double that mass but has a diameter just half that of Earth. It also rotates once every 13 seconds, the fastest of any known white dwarf.

The mass determination is reliable because the XMM-Newton tracking data allowed the astronomers to use the most robust method for ‘weighing’ a star, one that uses the gravitational physics devised by Isaac Newton in the 17th century. Most likely, the white dwarf has grown to its unusual mass by stealing gas from its companion star, a process known as accretion. At 1.3 solar masses, the white dwarf is now close to a dangerous limit.

When it grows larger than 1.4 solar masses, a white dwarf is thought either to explode or collapse to form an even more compact object called a neutron star. The explosion of a white dwarf is the leading explanation for ‘type Ia supernovae’, bright events that are used as standard beacons by astronomers to measure the expansion of the Universe. Until now, astronomers have not been able to find an accreting white dwarf in a binary system where the mass could be determined so accurately.

“This is the Rosetta stone of white dwarfs in binary systems. Our precise determination of the masses of the two stars is crucial. We can now study it further and try to reconstruct its past, so that we can calculate its future,” says Mereghetti.

So start telling your descendants to watch out for the spectacular show! (And hopefully no new hoax emails will be spawned about a supernova coming soon that will look as big as the full Moon to the naked eye a la the “Mars as big as the full Moon” hoax!)

Lead image caption: Illustration of the white dwarf and its companion HD49798. If it was possible to look at the system up-close, it would look something like this. Credits: Francesco Mereghetti, background image: NASA, ESA and T.M. Brown (STScI)

Source: ESA


12 Responses

  1. Member
    IVAN3MAN says

    To show everybody that I actually read the articles and I don’t just look for typos, I would like to address an issue in the article:

    This particular white dwarf contains at least double that mass but has a diameter just half that of Earth. It also rotates once every 13 seconds, the fastest of any known white dwarf. […] At 1.3 solar masses, the white dwarf is now close to a dangerous limit.

    When it grows larger than 1.4 solar masses, a white dwarf is thought either to explode or collapse to form an even more compact object called a neutron star.

    That limit, known as the Chandrasekhar limit, applies to non-rotating white dwarfs; however, according to this paper, “Presupernova evolution of accreting white dwarfs with rotation [PDF]”, this limit may increase if the white dwarf is rotating rapidly and non-uniformly.

    From Wikipedia — Chandrasekhar limit:

    A type Ia supernova apparently from a supra-limit white dwarf

    On April 2003, the Supernova Legacy Survey observed a type Ia supernova, designated SNLS-03D3bb, in a galaxy approximately 4 billion light-years away. According to a group of astronomers at the University of Toronto and elsewhere, the observations of this supernova are best explained by assuming that it arose from a white dwarf which grew to twice the mass of the Sun before exploding. They believe that the star, dubbed the “Champagne Supernova” by David R. Branch, may have been spinning so fast that centrifugal force allowed it to exceed the limit. Alternatively, the supernova may have resulted from the merger of two white dwarfs, so that the limit was only violated momentarily. Nevertheless, they point out that this observation poses a challenge to the use of type Ia supernovae as standard candles.

  2. Hon. Salacious B. Crumb says

    HD 49798 / HIP 32502 is a 8.3v magnitude southern star in the constellation of Puppis, and is position at : RA 06h 48m 22 Dec. -44 deg 19′ 35″ some 2.5 degrees south-east of Nu Puppis. Based on the parallax of 1.16+/-0.63 milli arcseconds, the distance is about 862 parsecs or 2800 light-years from us.

    Let’s hope this object doesn’t blow in the near future, as the Gamma ray and emp pulse might no be such an enjoyable experience for those in southern ‘clines.

    Were it to happen, those in the far northern latitudes – above -56 degrees north would be totally safe from its radiation (at least for the next 2000 years or so, as the slow precession of the equinoxes might change that!) .

    Those hammered overhead by the radiation would like suffer considerably from a Supernova Type 2 this close. (Considering the Crab Nebula / M1 in Taurus lies about 2000 parsecs away !)
    as for Denotation Day, well it depends on the mass of the white dwarf. The precision of 1.3 solar masses means it will be ages in the future. Assuming a transfer rate of 10^-6 solar masses per year, would be 100,000 years from now. (Roughly the greatest transfer rates known – most observed are around 10^-9 solar masses per year.) The denotation date is made more complicated as the mass for the companion feeding the accretion disk – mostly hydrogen – can ignite and be thrown off a shell of material as a nova. This can also happen a couple of times, reacting as a recurrent nova. Such events could extend denotation day for millions of years (Assuming the normal star orbiting it would last so long.

    The other alternative possibility is the star and white dwarf could merge some time in the future- though this depends on the period around each other or whether the star at the end of its evolution swells enough when it expands as a red giant and swallows the white dwarf. This latter scenario would be enough to set off the “firecracker”.

    However, there is also an error in the order of 0.3 or 0.4 solar masses, which is made worst by the fact that the 1.4 solar masses of the Chandrasaker Limit is also still slightly inaccurate. I.e. around 1.44+/-0.2 solar masses. Worst this limit is based on a number of general assumptions too I.e. The composition of the fused materials left with the white dwarf.
    Nice article Nancy, even though the view is a bit simplistic – especially in view of expected responses from the fringe elements and the nutters.
    Those like our dear Anaconda, at least have nothing to worry about, as they don’t believe in dense stars like white dwarfs.

  3. Hon. Salacious B. Crumb says

    Oops!!

    I said; “Those hammered overhead by the radiation would like suffer considerably from a Supernova Type 2 this close.

    This is, of course, simply wrong.

    I meant a Supernovae Type 1 !!

    Apologies.

  4. Torbjorn Larsson OM says

    IVAN3MAN, that’s putting severe spin on it. AFAIU the 2 times Sun mass limit is the result from actual mass accretion processes in binaries, in idealized model cases it seems it can be 4 (!) times. Perhaps processes exist that goes into that regime as well.

    Btw, that paper mentions a connection between presupernova instabilities and gravitational wave radiation. When will such a binary spinup dwarf start to emit something that _may_ trigger detectors? I.e. is this close dwarf a candidate for GW detection?

  5. ILOVETHESTAR says

    Hon. Salacious B. Crumb -thank you for the info, I learn much when you post!!!!!

  6. Pvt.Pantzov says

    yeah, it was an interesting and informative comment/explanation.

    too bad it was tainted at the end with the customary anaconda trolling.

  7. Hon. Salacious B. Crumb says

    Pvt.Pantzov said:

    Yeah, it was an interesting and informative comment/explanation.
    too bad it was tainted at the end with the customary anaconda trolling.

    Tainted? Trolling? How stupid are you? My statement is actually true. Frankly nipping the alternative nonsense attacks before they start is the only way to sink these dingbats. Don’t like it, don’t read it.

  8. Dark Gnat says

    If the white dwarf does explode, what would happen to the companion star?

  9. Member
    IVAN3MAN says

    @ Dark Gnat,

    I can’t say for sure, but there is an illustration (1093 x 800 pixels) from ESO of SN 2006X, before and after the Type Ia Supernova Explosion, and an explanation of the event here:
    eso.org/public/outreach/press-rel/pr-2007/phot-31-07.html

  10. Duncan Ivry says

    Hon. Salacious B. Crumb: “Tainted? Trolling? How stupid are you? My statement is actually true. Frankly nipping the alternative nonsense attacks before they start is the only way to sink these dingbats. Don’t like it, don’t read it.”

    I have a completely different opinion about this, as I have already said in the past: Your way of attacking those “special” people is not appropriate. By mentioning them again and again and again — even before anything had happened at all — they win again and again and again. Above that, insulting other participants — e.g. calling them stupid — goes against the comment policy stating:

    “Be nice … I think you know when you’re being rude. Stop it.”

    “Don’t like it, don’t read it” does not work, because others have to read before they realize, what kind of statement it is. I don’t want to read your noise — just as much as I don’t want to read the noise produced by those “special” people. I would prefer you to stay away from the comment sections of Universe Today for a while.

    Remember, what a certain Hon. Salacious B. Crumb answered on April 24th, 2009 at 10:28 pm:
    I am pleased with you decision to moderate Universe Today, and support your move to remove “alternative theory” which has predominated this site for last five months or so.
    Hopefully, some of the irrelevancies by several here might encourage other to have an opportunity to ask questions and not be intimidated by the fringe elements.
    Regarding conforming to the rules, it might be advisable to point out issues in comments for a week or two and then start implementing immediate deletions.
    Anyway, hopefully the “out there” comments will now settle down.

  11. Hon. Salacious B. Crumb says

    As Duncan Ivry properly pointed out…

    Remember, what a certain Hon. Salacious B. Crumb answered on April 24th, 2009 at 10:28 pm:

    I am pleased with you decision to moderate Universe Today, and support your move to remove “alternative theory” which has predominated this site for last five months or so.
    Hopefully, some of the irrelevancies by several here might encourage other to have an opportunity to ask questions and not be intimidated by the fringe elements.
    Regarding conforming to the rules, it might be advisable to point out issues in comments for a week or two and then start implementing immediate deletions.
    Anyway, hopefully the “out there” comments will now settle down.

    Yeah. But this was before Anaconda started describing us “pigs”, and sillily disclosed his own agenda of trying to get people to join his crazy cause.
    In the wake of the deliberate misery this individual has created – well I totally agree with the Australian aborigine’s time-honoured judicial system known as “payback.” – something which Anaconda (Mark) is now actually learning to appreciate.

  12. Lawrence B. Crowell says

    The physics of SNi’s and the Chandrasekhar limit for degenerate electron physics in white dwarf stars is adjusted by athe angular momentum of such stars. This imposes error bars with the cosmological standard candle. It does not mean that observed luminosity drop with increasing distance is wrong. That would presume there is some consistent change in physical or “chemical” properties of white dwarfs the further out we look. That is a more problematic assumption than interpreting the data as evidence for accelerated expansion.

    LC

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