Featured Research

from universities, journals, and other organizations

Magnetar formation mystery solved? Supernova explosions and dizzying spins in a binary system

Date:
May 14, 2014
Source:
European Southern Observatory - ESO
Summary:
Magnetars are the bizarre super-dense remnants of supernova explosions. They are the strongest magnets known in the universe — millions of times more powerful than the strongest magnets on Earth. Astronomers now believe they’ve found the partner star of a magnetar for the first time. This discovery helps to explain how magnetars form — a conundrum dating back 35 years — and why this particular star didn’t collapse into a black hole as astronomers would expect.

This artist's impression shows the magnetar in the very rich and young star cluster Westerlund 1. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns. European astronomers have for the first time demonstrated that this magnetar -- an unusual type of neutron star with an extremely strong magnetic field -- probably was formed as part of a binary star system. The discovery of the magnetar's former companion elsewhere in the cluster helps solve the mystery of how a star that started off so massive could become a magnetar, rather than collapse into a black hole.
Credit: ESO/L. Cal็ada

Magnetars are the bizarre super-dense remnants of supernova explosions. They are the strongest magnets known in the Universe -- millions of times more powerful than the strongest magnets on Earth. A team of European astronomers using ESO's Very Large Telescope (VLT) now believe they've found the partner star of a magnetar for the first time. This discovery helps to explain how magnetars form -- a conundrum dating back 35 years -- and why this particular star didn't collapse into a black hole as astronomers would expect.

When a massive star collapses under its own gravity during a supernova explosion it forms either a neutron star or black hole. Magnetars are an unusual and very exotic form of neutron star. Like all of these strange objects they are tiny and extraordinarily dense -- a teaspoon of neutron star material would have a mass of about a billion tonnes -- but they also have extremely powerful magnetic fields. Magnetar surfaces release vast quantities of gamma rays when they undergo a sudden adjustment known as a starquake as a result of the huge stresses in their crusts.

The Westerlund 1 star cluster [1], located 16,000 light-years away in the southern constellation of Ara (the Altar), hosts one of the two dozen magnetars known in the Milky Way. It is called CXOU J164710.2-455216 and it has greatly puzzled astronomers.

"In our earlier work we showed that the magnetar in the cluster Westerlund 1 must have been born in the explosive death of a star about 40 times as massive as the Sun. But this presents its own problem, since stars this massive are expected to collapse to form black holes after their deaths, not neutron stars. We did not understand how it could have become a magnetar," says Simon Clark, lead author of the paper reporting these results.

Astronomers proposed a solution to this mystery. They suggested that the magnetar formed through the interactions of two very massive stars orbiting one another in a binary system so compact that it would fit within the orbit of the Earth around the Sun. But, up to now, no companion star was detected at the location of the magnetar in Westerlund 1, so astronomers used the VLT to search for it in other parts of the cluster. They hunted for runaway stars -- objects escaping the cluster at high velocities -- that might have been kicked out of orbit by the supernova explosion that formed the magnetar. One star, known as Westerlund 1-5 [2], was found to be doing just that.

"Not only does this star have the high velocity expected if it is recoiling from a supernova explosion, but the combination of its low mass, high luminosity and carbon-rich composition appear impossible to replicate in a single star -- a smoking gun that shows it must have originally formed with a binary companion," adds Ben Ritchie (Open University), a co-author on the new paper.

This discovery allowed the astronomers to reconstruct the stellar life story that permitted the magnetar to form, in place of the expected black hole [3]. In the first stage of this process, the more massive star of the pair begins to run out of fuel, transferring its outer layers to its less massive companion -- which is destined to become the magnetar -- causing it to rotate more and more quickly. This rapid rotation appears to be the essential ingredient in the formation of the magnetar's ultra-strong magnetic field.

In the second stage, as a result of this mass transfer, the companion itself becomes so massive that it in turn sheds a large amount of its recently gained mass. Much of this mass is lost but some is passed back to the original star that we still see shining today as Westerlund 1-5.

"It is this process of swapping material that has imparted the unique chemical signature to Westerlund 1-5 and allowed the mass of its companion to shrink to low enough levels that a magnetar was born instead of a black hole -- a game of stellar pass-the-parcel with cosmic consequences!" concludes team member Francisco Najarro (Centro de Astrobiologํa, Spain).

It seems that being a component of a double star may therefore be an essential ingredient in the recipe for forming a magnetar. The rapid rotation created by mass transfer between the two stars appears necessary to generate the ultra-strong magnetic field and then a second mass transfer phase allows the magnetar-to-be to slim down sufficiently so that it does not collapse into a black hole at the moment of its death.

Notes:

[1] The open cluster Westerlund 1 was discovered in 1961 from Australia by Swedish astronomer Bengt Westerlund, who later moved from there to become ESO Director in Chile (1970-74). This cluster is behind a huge interstellar cloud of gas and dust, which blocks most of its visible light. The dimming factor is more than 100,000, and this is why it has taken so long to uncover the true nature of this particular cluster.

Westerlund 1 is a unique natural laboratory for the study of extreme stellar physics, helping astronomers to find out how the most massive stars in the Milky Way live and die. From their observations, the astronomers conclude that this extreme cluster most probably contains no less than 100,000 times the mass of the Sun, and all of its stars are located within a region less than 6 light-years across. Westerlund 1 thus appears to be the most massive compact young cluster yet identified in the Milky Way galaxy.

All the stars so far analysed in Westerlund 1 have masses at least 30-40 times that of the Sun. Because such stars have a rather short life -- astronomically speaking -- Westerlund 1 must be very young. The astronomers determine an age somewhere between 3.5 and 5 million years. So, Westerlund 1 is clearly a newborn cluster in our galaxy.

[2] The full designation for this star is Cl* Westerlund 1 W 5.

[3] As stars age, their nuclear reactions change their chemical make-up -- elements that fuel the reactions are depleted and the products ofthe reactions accumulate. This stellar chemical fingerprint is first rich in hydrogen and nitrogen but poor in carbon and it is only very late in the lives of stars that carbon increases, by which point hydrogen and nitrogen will be severely reduced -- it is thought to be impossible for single stars to be simultaneously rich in hydrogen, nitrogen and carbon, as Westerlund 1-5 is.


Story Source:

The above story is based on materials provided by European Southern Observatory - ESO. Note: Materials may be edited for content and length.


Journal Reference:

  1. J. S. Clark et al. A VLT/FLAMES survey for massive binaries in Westerlund 1: IV.Wd1-5 binary product and a pre-supernova companion for the magnetar CXOU J1647-45. Astronomy and Astrophysics, 2014 (in press)

Cite This Page:

European Southern Observatory - ESO. "Magnetar formation mystery solved? Supernova explosions and dizzying spins in a binary system." ScienceDaily. ScienceDaily, 14 May 2014. <www.sciencedaily.com/releases/2014/05/140514084500.htm>.
European Southern Observatory - ESO. (2014, May 14). Magnetar formation mystery solved? Supernova explosions and dizzying spins in a binary system. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2014/05/140514084500.htm
European Southern Observatory - ESO. "Magnetar formation mystery solved? Supernova explosions and dizzying spins in a binary system." ScienceDaily. www.sciencedaily.com/releases/2014/05/140514084500.htm (accessed July 23, 2014).

Share This




More Space & Time News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Cargo Craft Undocks from Space Station

Raw: Cargo Craft Undocks from Space Station

AP (July 22, 2014) — A Russian Soyuz cargo-carrying spacecraft undocked from the International Space Station on Monday. The craft is due to undergo about ten days of engineering tests before it burns up in the Earth's atmosphere. (July 22) Video provided by AP
Powered by NewsLook.com
NASA Ceremony Honors Moon Walker Neil Armstrong

NASA Ceremony Honors Moon Walker Neil Armstrong

AP (July 21, 2014) — NASA honored one of its most famous astronauts Monday by renaming a historic building at the Kennedy Space Center in Florida. It now bears the name of Neil Armstrong, the first man to walk on the moon. (July 21) Video provided by AP
Powered by NewsLook.com
Neil Armstrong's Post-Apollo 11 Life

Neil Armstrong's Post-Apollo 11 Life

Newsy (July 19, 2014) — Neil Armstrong gained international fame after becoming the first man to walk on the moon in 1969. But what was his life like after the historic trip? Video provided by Newsy
Powered by NewsLook.com
This Week @ NASA, July 18, 2014

This Week @ NASA, July 18, 2014

NASA (July 18, 2014) — Apollo 11 yesterday, Next Giant Leap tomorrow, Science instruments for Europa mission, and more... Video provided by NASA
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins