Astronomy Now Home
Home Magazine Resources Store

On Sale Now!

The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.

Top Stories

Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...

White dwarf binaries
set to merge

Posted: 17 November 2010

Bookmark and Share

A team of astronomers have uncovered a dozen double-star systems of which half are spiraling towards each other, set to explode as faint, 'underluminous' supernovae.

The astronomers were studying hypervelocity stars that are being kicked out of our Milky Way Galaxy when they made the serendipitous discovery of the binary white dwarfs, the hot dense remains of a Sun-like star packed into a volume the size of the Earth.

In about 100 million years the binary star system J0923+3028 will merge. Credit: Clayton Ellis (CfA).

These particular systems are unusual in that they are circling each other at a distance less than the radius of Sun, and are more lightweight than typical white dwarf stars that are composed of carbon and oxygen, instead primarily made up of helium.

“These white dwarfs have gone through a dramatic weight loss program,” says Carlos Allende Prieto of the Instituto de Astrofisica de Canarias in Spain. “These stars are in such close orbits that tidal forces, like those swaying the oceans on Earth, led to huge mass losses.”

The astronomers say that because they orbit so close to each other they are stirring up the space-time continuum, creating ripples known as gravitational waves, which carry away the stars' orbital energy, forcing them to spiral closer together.

The binary star system J0923+3028 consists of two white dwarfs: a visible star weighing 23 percent as much as our Sun and about four times the diameter of Earth, and an unseen companion weighing 44 percent of the Sun and about one Earth-diameter in size. The stars are currently separated by about 220,000 miles and orbit each other once per hour. Image: Clayton Ellis (CfA). .

The tightest binary pair discovered in this study is expected to merge in about 100 million year, but the merging of their combined mass is too low to trigger a supernova event. Instead, a more massive white dwarf will likely be left over, marked by a brief flash of light much fainter than typical supernovae explosions.

Lead author Warren Brown speculates that these merging binaries might be one source of a rare breed of 'underluminous' supernovae, which are one hundred times fainter than a normal Type Ia supernova and eject just one-fifth as much material.

“The rate at which our white dwarfs are merging is the same as the rate of underluminous supernovae, about one every 2,000 years,” he says. “While we can’t know for sure whether our merging white dwarfs will explode as underluminous supernovae, the fact that the rates are the same is highly suggestive.”

The discovery has tripled the number of known merging white-dwarf systems and will help astronomers learn more about how this breed of star evolve.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


© 2014 Pole Star Publications Ltd.