Astronomy Now Home
Home Magazine Sky Chart Resources Store

On Sale Now!



The September 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). The Astronomy Now iPad/iPhone editions are now available worldwide on the 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...
  READ MORE

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...
  READ MORE

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...
  READ MORE








Planets around white dwarfs?
GEMMA LAVENDER
ASTRONOMY NOW
Posted: 18 April 2011


Bookmark and Share

Astronomers are finding tantalising hints of planets around dead stars, it was revealed today at the Royal Astronomical Society’s National Astronomy Meeting in Llandudno, Wales.

“We hit upon this idea of looking for planets around white dwarfs in a paper in 2002 by myself and colleagues,” says Dr. Matt Burleigh at the University of Leicester, who presented the latest results.


Do white dwarfs have planets? This question was discussed on Day 1 of the National Astronomy Meeting 2011. Image: NASA.

When a dying star swells into a red giant and loses mass by ejecting its outer layers to leave behind a white dwarf, the orbits of any planets around the star (and which were not swallowed up by the red giant) will expand. It is this widening of orbits that improves our ability to detect them and allowed Burleigh and his colleagues to use direct imaging and spectroscopy to hunt for exoplanets around these stars, which are common in our solar neighbourhood.

Burleigh, along with Fraser Clarke of Oxford University and Emma Hogan of the Gemini South Observatory, named the search for planets around white dwarfs the Degenerate Objects around Degenerate Objects Project, or DODO. Their strategy is to sample around 40 young white dwarfs within 65 light years. Deep, wide-field images in the near-infrared using Gemini and the Very Large Telescope in Chile were obtained where the common proper motion of companions is being analysed over one to three years in order to confirm if they are indeed orbiting the white dwarfs. DODO is sensitive to a few Jupiter masses.

Any planetary companions that orbit white dwarfs are believed to be mature gas giants with temperatures between –73 and 327 degrees Celsius (200 to 600 kelvin) and ages of up to several billion years.

In their hunt for planets around white dwarfs, the astronomers came across Gliese 3483, a system containing a white dwarf of 0.62 solar masses. Burleigh has noted that the star has a companion, but whether it is a planet or a brown dwarf still remains a mystery. The evidence for the companion being a planet is its mass, which is estimated to be between six and ten times the mass of Jupiter. This is too small for your typical brown dwarf and since the temperature is between 37 and 107 degrees Celsius (310–380 kelvin) it would be by far the the coldest brown dwarf ever found (see our recent news story for the current record holder).

On the other hand, the companion’s distance from the star (2,500 times the distance between Earth and the Sun, which is 149.6 million kilometres or one astronomical unit) is too far from the star for it to be a planet. “Even if you work it backwards [shrinking, rather than widening the orbit], the original separation would have been around 700 astronomical units,” says Burleigh. Even this distance is too far for the formation of a planet. However, there is a caveat to this, says Burleigh.“It’s perfectly possible that the object formed closer and was thrown out or is on a highly eccentric orbit,” he says.

The question as to whether the white dwarf is a brown dwarf or planet is still up for debate.

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.
 GET YOUR COPY

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.
 GET YOUR COPY

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!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.