Featured Research

from universities, journals, and other organizations

Millisecond pulsar paradox: Stellar astrophysics helps explain behavior of fast rotating neutron stars in binary systems

Date:
February 2, 2012
Source:
Max-Planck-Gesellschaft
Summary:
Pulsars are among the most exotic celestial bodies known. They have diameters of about 20 kilometers, but at the same time roughly the mass of our sun. A sugar-cube sized piece of its ultra-compact matter on Earth would weigh hundreds of millions of tons. A sub-class of them, known as millisecond pulsars, spin up to several hundred times per second around their own axes. Previous studies reached the paradoxical conclusion that some millisecond pulsars are older than the universe itself. Now this paradox may be solved by computer simulations, new research shows.

Pulsars are among the most exotic celestial bodies known. They have diameters of about 20 kilometres, but at the same time roughly the mass of our sun. A sugar-cube sized piece of its ultra-compact matter on Earth would weigh hundreds of millions of tons. A sub-class of them, known as millisecond pulsars, spin up to several hundred times per second around their own axes. Previous studies reached the paradoxical conclusion that some millisecond pulsars are older than the universe itself.
Credit: NASA / Goddard Space Flight Center / Dana Berry

Pulsars are among the most exotic celestial bodies known. They have diameters of about 20 kilometres, but at the same time roughly the mass of our sun. A sugar-cube sized piece of its ultra-compact matter on Earth would weigh hundreds of millions of tons. A sub-class of them, known as millisecond pulsars, spin up to several hundred times per second around their own axes. Previous studies reached the paradoxical conclusion that some millisecond pulsars are older than the universe itself.

Astrophysicist Thomas Tauris from the Max Planck Institute for Radio Astronomy and the Argelander Institute for Astronomy in Bonn could resolve this paradox by computer simulations. Through numerical calculations on the base of stellar evolution and accretion torques, he demonstrated that millisecond pulsars lose about half of their rotational energy during the final stages of the mass-transfer process before the pulsar turns on its radio beam. This result is in agreement with current observations and the findings also explain why radio millisecond pulsars appear to be much older than the white dwarf remnants of their companion stars -- and perhaps why no sub-millisecond radio pulsars exist at all. The results are reported in the February 03 issue of the journal "Science."

Millisecond pulsars are strongly magnetized, old neutron stars in binary systems which have been spun up to high rotational frequencies by accumulating mass and angular momentum from a companion star. Today we know of about 200 such pulsars with spin periods between 1.4 to 10 milliseconds. These are located in both the Galactic Disk and in Globular Clusters.

Since the first millisecond pulsar was detected in 1982, it has remained a challenge for theorists to explain their spin periods, magnetic fields and ages. For example, there is the "turn-off" problem, i.e. what happens to the spin of the pulsar when the donor star terminates its mass-transfer process?

"We have now, for the first time, combined detailed numerical stellar evolution models with calculations of the braking torque acting on the spinning pulsar," says Thomas Tauris, the author of the present study. "The result is that the millisecond pulsars lose about half of their rotational energy in the so-called Roche-lobe decoupling phase." This phase describes the termination of the mass transfer in the binary system. Hence, radio-emitting millisecond pulsars should spin slightly slower than their progenitors, X-ray emitting millisecond pulsars which are still accreting material from their donor star. This is exactly what the observational data seem to suggest. Furthermore, these new findings help explain why some millisecond pulsars appear to have characteristic ages exceeding the age of the Universe and perhaps why no sub-millisecond radio pulsars exist.

The key feature of the new results is that it has now been demonstrated how the spinning pulsar is able to break out of its so-called equilibrium spin. At this epoch the mass-transfer rate decreases which causes the magnetospheric radius of the pulsar to expand and thereby expel the collapsing matter like a propeller. This causes the pulsar to lose additional rotational energy and thus slow down its spin rate.

"Actually, without a solution to the "turn-off" problem we would expect pulsars to even slow down to spin periods of 50 to 100 milliseconds during the Roche-lobe decoupling phase," concludes Thomas Tauris. "That would be in clear contradiction with observational evidence for the existence of millisecond pulsars."


Story Source:

The above story is based on materials provided by Max-Planck-Gesellschaft. Note: Materials may be edited for content and length.


Journal Reference:

  1. T. M. Tauris. Spin-Down of Radio Millisecond Pulsars at Genesis. Science, 2012; 335 (6068): 561 DOI: 10.1126/science.1216355

Cite This Page:

Max-Planck-Gesellschaft. "Millisecond pulsar paradox: Stellar astrophysics helps explain behavior of fast rotating neutron stars in binary systems." ScienceDaily. ScienceDaily, 2 February 2012. <www.sciencedaily.com/releases/2012/02/120202151436.htm>.
Max-Planck-Gesellschaft. (2012, February 2). Millisecond pulsar paradox: Stellar astrophysics helps explain behavior of fast rotating neutron stars in binary systems. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2012/02/120202151436.htm
Max-Planck-Gesellschaft. "Millisecond pulsar paradox: Stellar astrophysics helps explain behavior of fast rotating neutron stars in binary systems." ScienceDaily. www.sciencedaily.com/releases/2012/02/120202151436.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