Subscribe free to our newsletters via your
. 24/7 Space News .

The Star That Should Not Exist
by Staff Writers
Munich, Germany (SPX) Jan 17, 2014

At the centre of this picture is a very unremarkable looking faint star, too faint to be seen through all but the largest amateur telescopes. This ancient star, in the constellation of Leo (The Lion), is called SDSS J102915+172927 and has been found to have the lowest amount of elements heavier than helium of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old. Image courtesy ESO/Digitized Sky Survey 2. For a larger version of this image please go here.

A team of European astronomers has used ESO's Very Large Telescope (VLT) to track down a star in the Milky Way that many thought was impossible. They discovered that this star is composed almost entirely of hydrogen and helium, with only remarkably small amounts of other chemical elements in it. This intriguing composition places it in the "forbidden zone" of a widely accepted theory of star formation, meaning that it should never have come into existence in the first place. The results will appear in the 1 September 2011 issue of the journal Nature.

A faint star in the constellation of Leo (The Lion), called SDSS J102915+172927 [1], has been found to have the lowest amount of elements heavier than helium (what astronomers call "metals") of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old.

"A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn't exist because the clouds of material from which they formed could never have condensed," [2] said Elisabetta Caffau (Zentrum fur Astronomie der Universitat Heidelberg, Germany and Observatoire de Paris, France), lead author of the paper. "It was surprising to find, for the first time, a star in this 'forbidden zone', and it means we may have to revisit some of the star formation models."

The team analysed the properties of the star using the X-shooter and UVES instruments on the VLT [3]. This allowed them to measure how abundant the various chemical elements were in the star. They found that the proportion of metals in SDSS J102915+172927 is more than 20 000 times smaller than that of the Sun [4][5].

"The star is faint, and so metal-poor that we could only detect the signature of one element heavier than helium - calcium - in our first observations," said Piercarlo Bonifacio (Observatoire de Paris, France), who supervised the project. "We had to ask for additional telescope time from ESO's Director General to study the star's light in even more detail, and with a long exposure time, to try to find other metals."

Cosmologists believe that the lightest chemical elements - hydrogen and helium - were created shortly after the Big Bang, together with some lithium [6], while almost all other elements were formed later in stars. Supernova explosions spread the stellar material into the interstellar medium, making it richer in metals. New stars form from this enriched medium so they have higher amounts of metals in their composition than the older stars. Therefore, the proportion of metals in a star tells us how old it is.

"The star we have studied is extremely metal-poor, meaning it is very primitive. It could be one of the oldest stars ever found," adds Lorenzo Monaco (ESO, Chile), also involved in the study.

Also very surprising was the lack of lithium in SDSS J102915+172927. Such an old star should have a composition similar to that of the Universe shortly after the Big Bang, with a few more metals in it. But the team found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang.

"It is a mystery how the lithium that formed just after the beginning of the Universe was destroyed in this star." Bonifacio added.

The researchers also point out that this freakish star is probably not unique. "We have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927. We are now planning to observe them with the VLT to see if this is the case," concludes Caffau.

[1] The star is catalogued in the Sloan Digital Sky Survey or SDSS. The numbers refer to the object's position in the sky.

[2] Widely accepted star formation theories state that stars with a mass as low as SDSS J102915+172927 (about 0.8 solar masses or less) could only have formed after supernova explosions enriched the interstellar medium above a critical value. This is because the heavier elements act as "cooling agents", helping to radiate away the heat of gas clouds in this medium, which can then collapse to form stars. Without these metals, the pressure due to heating would be too strong, and the gravity of the cloud would be too weak to overcome it and make the cloud collapse. One theory in particular identifies carbon and oxygen as the main cooling agents, and in SDSS J102915+172927 the amount of carbon is lower than the minimum deemed necessary for this cooling to be effective.

[3] X-shooter and UVES are VLT spectrographs - instruments used to separate the light from celestial objects into its component colours and allow detailed analysis of the chemical composition. X-shooter can capture a very wide range of wavelengths in the spectrum of an object in one shot (from the ultraviolet to the near-infrared). UVES is the Ultraviolet and Visual Echelle Spectrograph, a high-resolution optical instrument.

[4] The star HE 1327-2326, discovered in 2005, has the lowest known iron abundance, but it is rich in carbon. The star now analysed has the lowest proportion of metals when all chemical elements heavier than helium are considered.

[5] ESO telescopes have been deeply involved in many of the discoveries of the most metal-poor stars. Some of the earlier results were reported in eso0228 and eso0723 and the new discovery shows that observations with ESO telescopes have let astronomers make a further step closer to finding the first generation of stars.

[6] Primordial nucleosynthesis refers to the production of chemical elements with more than one proton a few moments after the Big Bang. This production happened in a very short time, allowing only hydrogen, helium and lithium to form, but no heavier elements. The Big Bang theory predicts, and observations confirm, that the primordial matter was composed of about 75% (by mass) of hydrogen, 25% of helium, and trace amounts of lithium.

This research was presented in a paper, "An extremely primitive halo star", by Caffau et al. to appear in the 1 September 2011 issue of the journal Nature.


Related Links
Stellar Chemistry, The Universe And All Within It

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

Hubble Probes Interior of Tarantula Nebula
Baltimore MD (SPX) Jan 12, 2014
Like lifting a giant veil, the near-infrared vision of NASA's Hubble Space Telescope uncovers a dazzling new view deep inside the Tarantula Nebula. Hubble reveals a glittering treasure trove of more than 800,000 stars and protostars embedded inside the nebula. These observations were obtained as part of the Hubble Tarantula Treasury Program. When complete, the program will produce a ... read more

China's moon rover performs first lunar probe

Internet Radio Provides Musical Space-Weather Reports from NASA's LRO Mission

Moon rover, lander wake after lunar night

India to launch second mission to moon by 2017

A Decade in the Dust

An Engineer With His Sights on Mars

Lichen on Mars

Megafloods: What They Leave Behind

Commercial Spaceflight Federation Applauds Passage of Bill Providing Funding for Commercial Programs

NASA Tests Orion Spacecraft Parachute Jettison over Arizona

NASA Space Launch System Could Make 'Outside the Box' Science Missions Possible

NASA Sets Coverage Schedule for TDRS-L/Atlas V Launch Events

Official: China's space policy open to world

China launches communications satellite for Bolivia

China's moon rover continues lunar survey after photographing lander

China's Yutu "naps", awakens and explores

Cygnus Work Under Way, Normal Station Operations Continue

Spaceflight, Nanoracks Partnership Launch CubeSat Customers Towards Historic ISS Deployment

Orbital's cargo ship arrives at space station

Obama Administration Extends ISS Until at Least 2024

NASA's Commercial Crew Partners Aim to Capitalize, Expand on 2013 Successes in 2014

Ariane Flight VA217; Ariane Flight VA216 and Soyuz Flight VS07

2014 set to be a very productive year for collaboration between Arianespace and Italy

Vega Flight VV03 And Ariane Flight VA218

NASA's Kepler Provides Insights on Enigmatic Planets

Powerful Planet Finder Turns Its Eye to the Sky

New kind of planet or failed star? Astrophysicists discover category-defying celestial object

SF State astronomers discover new planet in Pisces constellation

ISS delays planned orbit raise due to space junk threat

IBM to invest $1.2 bn to expand 'cloud'

Space fishing: Japan to test 'magnetic net' for space junk

Boeing Space Surveillance System Reduces Risk of Satellite Loss by 66 Percent

The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal 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