Not All Star Nurseries Are Equal

EXO WORLDS

File Photo: Few features can be seen in N 81 from ground-based telescopes, earning it the informal nick-name "The Blob." Astronomers were not sure if just one or a few hot stars were embedded in the cloud, or if it was a stellar nursery containing a large number of less massive stars. Hubble's high-resolution imaging shows the latter to be the case, revealing that numerous young, white-hot stars---easily visible in the color picture---are contained within N 81. Hubble Heritage Project Image DESKTOP AVAILABLE

by Stuart Clark
Baltimore - Nov. 1, 2000
A survey of 35,000 distant stars has left planet-hunting astronomers empty-handed, despite predictions that they would find 17 new worlds.

The results, to be published in Astrophysical Journal Letters in December, have left astronomers seriously considering the notion that planet-forming conditions may not be uniform across galaxies.

Ron Gilliland of the Space Telescope Science Institute in Baltimore, Maryland, and Tim Brown at the US National Center for Atmospheric Research in Boulder, Colorado, used the Hubble Space Telescope to search the globular star cluster 47 Tucanae.

They looked for a tell-tale dip in brightness that can occur when a planet outside the Solar System passes in front of its star. Most of these exoplanets are "hot Jupiters"; gas giant globes that circle their stars closely, taking just a few days to complete an orbit.

Of the 50 identified planets outside our Solar System, only one is aligned to create this blinking effect when viewed from Earth. HD 209458 was first spotted winking at astronomers in November 1999. The Hubble astronomers observed this star to calibrate the effect before embarking upon their own fruitless search.

Ian Crawford at University College London believes the work could be significant. "Taken at face value, it means that planets are rarer around stars in globular clusters than they are around freely floating stars in the solar neighbourhood."

Heavy metal
The first results were presented at an American Astronomical Society meeting (New Scientist, 17 June 2000, p 12), but astronomers are now realising that they might have predicted the findings. Crawford explains: "It is becoming statistically significant that those stars found to have planets are rich in heavy elements. They looked at a very metal-poor globular cluster and it has got fewer planets than expected. It all makes sense."

Astronomers suspect that heavy elements provide a planetary "seed" dense enough to attract the gases characteristic of hot Jupiters. Jupiter itself is thought to have a heavy-element core 15 times the mass of the Earth.

Astronomers are considering other reasons why planet-forming conditions appear to vary across the Galaxy. The density of stars in a globular cluster is much greater than in the Sun's neighbourhood. This may have ripped planet-forming discs apart before planets could condense.

But Crawford is cautious not to draw too many conclusions from the findings. "They expected to see 17 planets and they have seen none. It does not mean that there are no planets there."

This article appeared in the Oct 31 issue of New Scientist New Scientist. Copyright 2000 - All rights reserved. The material on this page is provided by New Scientist and may not be published, broadcast, rewritten or redistributed without written authorization from New Scientist.

EXO WORLDS

Many Exo Planets Are Probably Stars

Pasadena - Oct. 29, 2000
More than half of the recently detected extrasolar planets appear not to be planetary objects at all, according to a preliminary astrometric study conducted by researchers at the University of Pittsburgh's Allegheny Observatory, the Lunar and Planetary Institute, and the Korea Astronomy Observatory. The study is being presented at the Division for Planetary Sciences of the American Astronomical Society meeting, October 23-27, in Pasadena, California.

Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor $5 Billed Once credit card or paypal		SpaceDaily Monthly Supporter $5 Billed Monthly paypal only

The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.