NASA's Chandra explores hidden population of exotic neutron stars

Washington, May 24 (ANI): A major campaign using NASA's Chandra X-ray Observatory and several other satellites has suggested that exotic neutron stars, magnetars may be more diverse-and common-than previously thought.

Magnetars-the dense remains of dead stars that erupt sporadically with bursts of high-energy radiation-are some of the most extreme objects known in the universe.

When a massive star runs out of fuel, its core collapses to form a neutron star, an ultradense object about 10 to 15 miles wide. The gravitational energy released in this process blows the outer layers away in a supernova explosion and leaves the neutron star behind.

Most neutron stars are spinning rapidly-a few times a second-but a small fraction have a relatively low spin rate of once every few seconds, while generating occasional large blasts of X-rays. Because the only plausible source for the energy emitted in these outbursts is the magnetic energy stored in the star, these objects are called "magnetars."

Most magnetars have extremely high magnetic fields on their surface that are ten to a thousand times stronger than for the average neutron star. New observations show that the magnetar known as SGR 0418+5729 (SGR 0418 for short) doesn't fit that pattern. It has a surface magnetic field similar to that of mainstream neutron stars.

"We have found that SGR 0418 has a much lower surface magnetic field than any other magnetar," said Nanda Rea of the Institute of Space Science in Barcelona, Spain.

"This has important consequences for how we think neutron stars evolve in time, and for our understanding of supernova explosions," Rea noted.

The researchers monitored SGR 0418 for over three years using Chandra, ESA's XMM-Newton as well as NASA's Swift and RXTE satellites. They were able to make an accurate estimate of the strength of the external magnetic field by measuring how its rotation speed changes during an X-ray outburst. These outbursts are likely caused by fractures in the crust of the neutron star precipitated by the build-up of stress in a relatively strong, wound-up magnetic field lurking just beneath the surface.

"This low surface magnetic field makes this object an anomaly among anomalies," said co-author GianLuca Israel of the National Institute of Astrophysics in Rome.

"A magnetar is different from typical neutron stars, but SGR 0418 is different from other magnetars as well," the researcher noted.

By modeling the evolution of the cooling of the neutron star and its crust, as well as the gradual decay of its magnetic field, the researchers estimated that SGR 0418 is about 550,000 years old. This makes SGR 0418 older than most other magnetars, and this extended lifetime has probably allowed the surface magnetic field strength to decline over time. Because the crust weakened and the interior magnetic field is relatively strong, outbursts could still occur.

The case of SGR 0418 may mean that there are many more elderly magnetars with strong magnetic fields hidden under the surface, implying that their birth rate is five to ten times higher than previously thought.

"We think that about once a year in every galaxy a quiet neutron star should turn on with magnetar-like outbursts, according to our model for SGR 0418," said Jose Pons of the University of Alacant in Spain.

Another implication of the model is that the surface magnetic field of SGR 0418 should have once been very strong at its birth a half million years ago. This, plus a possibly large population of similar objects, could mean that the massive progenitor stars already had strong magnetic fields, or these fields were created by rapidly rotating neutron stars in the core collapse that was part of the supernova event.

If large numbers of neutron stars are born with strong magnetic fields then a significant fraction of gamma-ray bursts might be caused by the formation of magnetars rather than black holes. Also, the contribution of magnetar births to gravitational wave signals-ripples in space-time-would be larger than previously thought.

These new results on SGR 0418 appear online and will be published in the June 10, 2013, issue of The Astrophysical Journal. (ANI)

Matches

MORE TOP STORIES TODAY

Mumbai Indians vs Kolkata Knight Riders

Mumbai Indians vs Kolkata Knight Riders

Abu Dhabi: Kallis and Pandey's half-centuries help Kolkata set Mumbai 164-run target. More »

Pietersen to miss Delhi's first game

Pietersen to miss Delhi's first game

The former England batsman will have to lead the franchise as he is out of the match against Bangalore with a finger injury. More »

Srinivasan named in fixing report: SC

Srinivasan named in fixing report: SC

The court emphasised that the tainted administrator can no longer work for the BCCI. More »

'If you do the wrong thing it will be found out'

'If you do the wrong thing it will be found out'

'Everyone knows what is right and what is wrong and if you do the wrong thing it will be found out' More »

Why I'm not looking forward to the IPL

Why I'm not looking forward to the IPL

Welcome to another season of a league that many watch but few trust. More »

Mitchell Johnson may quit T20s for Test cricket

Mitchell Johnson may quit T20s for Test cricket

Australia's Mitchell Johnson may quit limited-overs cricket to prolong his test career with an eye on the 2015 Ashes series in England, the fast bowler… More »

There's a lot going on: Fleming

There's a lot going on: Fleming

He experienced anxious moments in the lead-up to the tournament as the courts decided on whether to suspend the franchise, he said, but stressed that the… More »

Latif couldn’t work with tainted players

Latif couldn’t work with tainted players

Former Pakistan cricket captain Rashid Latif said Tuesday he turned down the job of national chief selector because he could not work with ex-players tainted… More »

We are not over-confident: Bailey

We are not over-confident: Bailey

Indian Premier League — George Bailey-led Kings XI Punjab will face Chennai Super Kings on Friday. More »

Big runs expected, with bat and ball

Big runs expected, with bat and ball

Royal Challengers Bangalore: Their main concern, once again, is the fast bowling More »

Taxing issue — BCCI hits roadblock

Taxing issue — BCCI hits roadblock

MoU between BCCI & its units to avoid double taxation delayed after a few decline to share details. More »

Black Caps pick rookie duo for West Indies

Black Caps pick rookie duo for West Indies

New Zealand selectors included two new caps in a 15-man Test squad named Tuesday to tour the West Indies, with injury-hit spinner Dan Vettori's future… More »

The stage is set for IPL-7 to start

The stage is set for IPL-7 to start

The Preview — Defending champions Mumbai Indians take on Kolkata Knight Riders More »

Srinivasan appeals to court to allow BCCI comeback

Srinivasan appeals to court to allow BCCI comeback

He was aggrieved by the allegations against him during the hearing. More »

India: cricket's Brazil

India: cricket's Brazil

They are tough to beat with a big talent base exposed to good facilities. (CYCSPL) More »

Delhi Daredevils say no to gifts

Delhi Daredevils say no to gifts

Franchises are doing their bit to refurbish the image of the tainted league. More »

Klinger on his exit from South Australia

Klinger on his exit from South Australia

Michael Klinger has revealed he felt compelled to leave South Australia after being told he would be only a fringe part of the Redbacks' plans for next season, and disputed the suggestion that he left… More »

India-Pakistan Test series likely in 2015

India-Pakistan Test series likely in 2015

The revival of Indo-Pak Test ties could take place in UAE. More »

Kohli hopes to end RCB trophy drought

Kohli hopes to end RCB trophy drought

'This time around we will hope to go few more steps ahead and actually get that trophy' More »

Gavaskar can help IPL regain glory

Gavaskar can help IPL regain glory

Apart from the foreign players a lot of behind-the-scene activity has taken place in selecting the Indian domestic players. More »

Tendulkar, Ganguly to promote soccer

Tendulkar, Ganguly to promote soccer

Leading Spanish club Atletico Madrid and former cricketers Sachin Tendulkar and Sourav Ganguly are among the owners of eight franchises of a new Indian… More »

This isn’t my first trip to India: Neesham

This isn’t my first trip to India: Neesham

Kiwi all-rounder wants to utilise the India leg to explore the country’s tourist attractions. More »

Ishant wanted to quit ODIs

Ishant wanted to quit ODIs

Says his mother made him change his mind. More »

Supreme Court says no to BCCI’s request

Supreme Court says no to BCCI’s request

Bench refuses to grant access to recordings of Srini and Dhoni’s depositions before Mudgal committee. More »