Two dying stars reborn as one (w/ video)

Apr 06, 2011
2 dying stars reborn as 1
CfA astronomers have found a pair of white dwarf stars orbiting each other once every 39 minutes. In a few million years, they will merge and reignite as a helium-burning star. In this artist's conception, the reborn star is shown with a hypothetical world. Credit: David A. Aguilar (CfA)

White dwarfs are dead stars that pack a Sun's-worth of matter into an Earth-sized ball. Astronomers have just discovered an amazing pair of white dwarfs whirling around each other once every 39 minutes. This is the shortest-period pair of white dwarfs now known. Moreover, in a few million years they will collide and merge to create a single star.

"These stars have already lived a full life. When they merge, they'll essentially be 'reborn' and enjoy a second life," said Smithsonian Mukremin Kilic (Harvard-Smithsonian Center for Astrophysics), lead author on the paper announcing the discovery.

Out of the 100 billion stars in the , only a handful of merging white dwarf systems are known to exist. Most were found by Kilic and his colleagues. The latest discovery will be the first of the group to merge and be reborn.

The newly identified binary star (designated SDSS J010657.39 – 100003.3) is located about 7,800 light-years away in the constellation Cetus. It consists of two white dwarfs, a visible star and an unseen companion whose presence is betrayed by the visible star's motion around it. The visible white dwarf weighs about 17 percent as much as the , while the second white dwarf weighs 43 per cent as much. Astronomers believe that both are made of helium.

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CfA astronomers have found a pair of white dwarf stars orbiting each other once every 39 minutes. In a few million years, they will merge and reignite as a helium-burning star. Credit: CfA

The two white dwarfs orbit each other at a distance of 140,000 miles - less than the distance from the to the Moon. They whirl around at speeds of 270 miles per second (1 million miles per hour), completing one orbit in only 39 minutes.

The fate of these stars is already sealed. Because they wheel around so close to each other, the white dwarfs stir the space-time continuum, creating expanding ripples known as gravitational waves. Those waves carry away orbital energy, causing the to spiral closer and closer together. In about 37 million years, they will collide and merge.

When some collide, they explode as a supernova. However, to explode the two combined have to weigh 40 percent more than our Sun. This white dwarf pair isn't heavy enough to go supernova. Instead, they will experience a second life. The merged remnant will begin fusing helium and shine like a normal star once more. We will witness starlight reborn.

This binary white dwarf was discovered as part of a survey program being conducted with the MMT Observatory on Mount Hopkins, Ariz. The survey has uncovered a dozen previously unknown white dwarf pairs. Half of those are merging and might explode as supernovae in the astronomically near future.

Explore further: Integral gamma-ray observatory demonstrates white dwarfs can reignite and explode as supernovae

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User comments : 14

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eachus
1.5 / 5 (2) Apr 06, 2011
How closely have they looked for the unseen companion star? Nothing says it can't be a very old, and dim white dwarf. But it could also be neutron star with most of the surrounding gas blown away or accreted onto the companion. Or it could be an object made of dark matter--a dark star would potentially start answering lots of questions about dark matter.
JonnyMcA
1 / 5 (1) Apr 06, 2011
A confusingly worded article. In one paragraph it states that the mass of the white dwarfs are 17% and 43 % more than the sun. Then it states that it wont go supernova because it the total mass of merging white dwarfs need to be a total of 40% greater than the sun. But 1.17 + 1.43 = 2.60 which is much greater than 1.4 solar masses.

Perhaps this apparent contradiction could be clarified?
Nik_2213
5 / 5 (5) Apr 06, 2011
Sorry, Jonny, your math is off: They say '17% & 43% *of*' ie 0.17 Solar Mass and 0.43 Solar Mass. Combined, they're well short of critical level...
Quantum_Conundrum
1 / 5 (4) Apr 06, 2011
Could be a brown dwarf of a microscopic black hole which has since grown some?
eachus
1 / 5 (1) Apr 06, 2011
Could be a brown dwarf of a microscopic black hole which has since grown some?


No, low temperatures near a black hole just don't happen. However, in this particular case, the heavier companion could be a black hole. If so Stephen Hawking will get a Nobel Prize. This object is much smaller than a black hole created by a supernova. Hawking in one of his early papers on black holes pointed out that sub-stellar mass black holes could have been created during the big bang. If this is such a black hole, it would indicate that a significant fraction of dark matter could be such sub-stellar black holes. Why no accretion disk? There might be a faint one, but by now astronomers are used to supermassive black holes turning off and on their jets and accretion disks.
Decimatus
not rated yet Apr 06, 2011
Somehow I doubt these stars just clump together and form some new and happy little life together.

Supernova or not, the few million years after they smack together is probably not going to be pretty for the surrounding solar system.
Ethelred
3.9 / 5 (7) Apr 06, 2011
. But it could also be neutron star with most of the surrounding gas blown away or accreted onto the companion.
Mass is too low to be a neutron star. Has to been around a long time to have reached the white dwarf stage with that low a mass.

Or it could be an object made of dark matter--a dark star would potentially start answering lots of questions about dark matter.
By that thinking it could be made of puppy dogs.

It is dark matter in the lower case sense. It is not Dark Matter in the sense of the stuff that seems to be involved in gravitational lensing.

Quantum_Conundrum
Could be a brown dwarf of a microscopic black hole which has since grown some?
That remark only wishes it was in the Bunny Rabbit class. Brown dwarf or black hole. Choose one because the two together would get you a black hole.

eachus
However, in this particular case, the heavier companion could be a black hole.
How? That is the one we can see.

Ethelred
soulman
3.7 / 5 (6) Apr 06, 2011
Supernova or not, the few million years after they smack together is probably not going to be pretty for the surrounding solar system.

I doubt the solar system is especially 'happy' right now, seeing as it has no main sequence star(s) now.

This system might be a good candidate for the proposed LISA mission to detect gravitational waves.
Decimatus
not rated yet Apr 07, 2011
Supernova or not, the few million years after they smack together is probably not going to be pretty for the surrounding solar system.

I doubt the solar system is especially 'happy' right now, seeing as it has no main sequence star(s) now.

This system might be a good candidate for the proposed LISA mission to detect gravitational waves.


Well there have been some recent stories about habitable zones around white dwarfs, so I can see certain planets in the neighborhood.

Anyway, more specifically I am thinking that there will be a time preceding the final coupling where a significant bridge of matter forms between these two stars and vast solar eruptions blanket everything within billions of miles.

Also, I can imagine some interesting stellar happenings if both stars had significantly sized cores of heavy elements and how those 2 cores may or may not mesh very well.
JonnyMcA
5 / 5 (2) Apr 07, 2011
Sorry, Jonny, your math is off: They say '17% & 43% *of*' ie 0.17 Solar Mass and 0.43 Solar Mass. Combined, they're well short of critical level...


Thanks Nik, the error was mine, as I mis-read it. Thanks for clearing that up.
Ethelred
3.9 / 5 (7) Apr 07, 2011
eachus

However, in this particular case, the heavier companion could be a black hole.

How? That is the one we can see.
Sorry, I just noticed that part was still in there. I wrote it thinking the heavier star HAD to be the visible one, checked and found it was wrong, the heavier star is the one we can't see. I THOUGHT I deleted it before posting.

Weird that the heavier one is the one we don't see.

I screwed up. Not the first time.

Sorry.

Ethelred
SteWe
not rated yet Apr 07, 2011
... maybe they meant "0.17 and 0.43*0.17 solar masses, respectivly".
Though I wonder how such low mass stars can be white dwarfs already - I would have guessed that red dwarves of that size burn nearly as long as the universe might live ... !??!
Quantum_Conundrum
1 / 5 (1) Apr 07, 2011
The "f" was a typo, I wrote "Brown dwarf OR microscopic black hole".

The more massive object is the invisible one, so that only leaves a few candidates:

Brown dwarf (possibly heavy metal core of a dead star)
Black hole
Incredibly dim Red Dwarf (how? 0.4M should have some light...)

A brown Dwarf or Red Dwarf should show up on an Infrared telescope, so all they'd have to do to find it is point some of our best infrared and radio telescopes at it and they'd see it...certainly the James Webb would see it once it gets deployed...

If it is a sub-stellar or microscopic black hole it is possible for it not to have an acretion disk simply because the two objects may have already eaten all of the available matter, and they aren't close enough yet for the white dwarf to be destroy and pulled into an acretion disk yet...

If it is a black hole, then it will either show up on an x-ray telescope due to some acretion, OR it won't show up on anything at all, except the gravity...
yyz
5 / 5 (6) Apr 07, 2011
Besides being the shortest period detached WD known, this system also presents the first observation of a tidally distorted WD, revealed through high speed photometry.

Future high speed photometry on larger scopes should help constrain the inclination of this system (leading to a better mass estimate for the companion). These observations could also be used to search for possible grazing eclipses in this system, which, if found, could provide further details about the two stars. The authors estimate there is a 25% chance of grazing eclipses occurring in this system.

"This system might be a good candidate for the proposed LISA mission to detect gravitational waves."

The paper notes that this system lies at the limits of detection by LISA (after a year of observations) and given improved ephemerides, may be detectable above the galactic background noise after a few years of observation: http://arxiv.org/...54v1.pdf