Evolved stars locked in fatalistic dance

Jul 13, 2011
Two white dwarfs have been discovered on the brink of a merger. In just 900,000 years, material will start to stream from one star to the other (as shown in this artist's conception), beginning the process that may end with a spectacular supernova explosion. Watching these stars fall in will allow astronomers to test Einstein's theory of general relativity as well as the origin of a special class of supernovae. Credit: David A. Aguilar (CfA)

White dwarfs are the burned-out cores of stars like our Sun. Astronomers have discovered a pair of white dwarfs spiraling into one another at breakneck speeds. Today, these white dwarfs are so near they make a complete orbit in just 13 minutes, but they are gradually slipping closer together. About 900,000 years from now - a blink of an eye in astronomical time - they will merge and possibly explode as a supernova. By watching the stars converge, scientists will test both Einstein's theory of general relativity and the origin of some peculiar supernovae.

The two white dwarfs are circling at a bracing speed of 370 miles per second (600 km/s), or 180 times faster than the fastest jet on Earth.

"I nearly fell out of my chair at the telescope when I saw one star change its speed by a staggering 750 miles per second in just a few minutes," said Smithsonian astronomer Warren Brown, lead author of the paper reporting the find.

The brighter white dwarf contains about a quarter of the Sun's mass compacted into a Neptune-sized ball, while its companion has more than half the and is Earth-sized. A penny made of this white dwarf's material would weigh about 1,000 pounds on Earth.

Their mutual is so strong that it deforms the lower-mass star by three percent. If the Earth bulged by the same amount, we would have tides 120 miles high.

The discovery team has been hunting for pairs of using the MMT telescope at the Whipple Observatory on Mt. Hopkins, Arizona. These star pairs are too close together to distinguish photographically. By looking at the spectra, however, Brown and his team were able to differentiate the two and measure their relative motions. These stars are also oriented such that they eclipse each other every 6 minutes.

"If there were aliens living on a planet around this , they would see one of their two suns disappear every 6 minutes - a fantastic light show." said Smithsonian astronomer and co-author Mukremin Kilic.

These eclipses provide a very accurate clock, which is extremely useful for measuring any changes in the system.

General relativity predicts that moving objects will create ripples in the fabric of space-time, called gravitational waves. These waves carry away energy, causing the stars to inch closer together and orbit each other faster and faster.

"Though we have not yet directly measured gravitational waves with modern instruments, we can test their existence by measuring the change in the separation of these two stars," said co-author J. J. Hermes, a graduate student at the University of Texas at Austin. "Because they don't seem to be exchanging mass, this system is an exceptionally clean laboratory to perform such a test."

The team expects to conduct this test in a few months, when the star pair emerges from behind the Sun as seen from Earth.

Some models predict merging white dwarf pairs such as these are the source of a rare class of unusually faint stellar explosions called underluminous .

"If these systems are responsible for underluminous supernovae, we will detect these binary white dwarf systems with the same frequency that we see the supernovae. Our survey isn't complete, but so far, the numbers agree," said Brown.

This work will provide an important observational test on theories of white dwarf mergers, which are thought to produce many kinds of supernovae, not just the underluminous type.

Explore further: Thermonuclear X-ray bursts on neutron stars set speed record

Related Stories

Two dying stars reborn as one (w/ video)

Apr 06, 2011

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 ...

Binary white dwarf stars

May 04, 2011

(PhysOrg.com) -- When a star like our sun gets to be very old, after another seven billion years or so, it will no longer be able to sustain burning its nuclear fuel.

Stars Flood Space with Gravitational Waves

May 30, 2005

A scientist using NASA's Chandra X-ray Observatory has found evidence that two white dwarf stars are orbiting each other in a death grip, destined to merge. The data indicate gravitational waves are carrying energy away fro ...

Hubble 'weighs' Dog Star's companion

Dec 13, 2005

For astronomers, it's always been a source of frustration that the nearest white-dwarf star is buried in the glow of the brightest star in the nighttime sky. This burned-out stellar remnant is a faint companion ...

Recommended for you

Spitzer telescope witnesses asteroid smashup

23 hours ago

(Phys.org) —NASA's Spitzer Space Telescope has spotted an eruption of dust around a young star, possibly the result of a smashup between large asteroids. This type of collision can eventually lead to the ...

Witnessing the early growth of a giant

Aug 27, 2014

Astronomers have uncovered for the first time the earliest stages of a massive galaxy forming in the young Universe. The discovery was made possible through combining observations from the NASA/ESA Hubble ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

Donutz
4 / 5 (3) Jul 13, 2011
So the stars are fatalistic. They have a belief system.

Dictionary is your friend.
tadchem
5 / 5 (1) Jul 13, 2011
I would like to see the method they intend to use to deconvolute energy losses due to gravitational radiation from energy losses due to tidal friction. Measuring the latter would require simultaneously obtaining the speed of rotation of each star.
SemiNerd
5 / 5 (1) Jul 13, 2011
tadchem - I thought of the same thing, but both effects can be relatively easily calculated. That's how they came up with theb 900,000 year number.
rubberman
1 / 5 (1) Jul 13, 2011
I would like to see the ocean that can generate a 120 mile high wave......
Grizzled
5 / 5 (1) Jul 13, 2011
No big deal Rubberman - given enough gravitational pull our own oceans could, they have enough water in them. Of course, that would mean leaving huge expances of the ocean floor bare but who cares - we wouldn't be around to see it anyway.