Featured Research

from universities, journals, and other organizations

Scientists Gain Glimpse Of Bizarre Matter In A Neutron Star

September 21, 2004
NASA/Goddard Space Flight Center
Scientists have obtained their best measurement yet of the size and contents of a neutron star, an ultra-dense object containing the strangest and rarest matter in the Universe.

This image is taken from a computer artist's concept that illustrates a thermonuclear burst consuming an entire neutron star. Neutron star EXO 0748-676 (blue sphere) is part of a binary star system, and its neighboring star (yellow-red sphere) supplies the fuel for the thermonuclear bursts. During solar outbursts or when the orbit brings the stars closer together, gas from the companion star flows toward the neutron star, attracted by its strong gravity. The flow of gas forms a swirling disk around the neutron star, called an accretion disk (multi-colored swirl around the blue sphere).

Scientists have obtained their best measurement yet of the size and contents of a neutron star, an ultra-dense object containing the strangest and rarest matter in the Universe.

Related Articles

This measurement may lead to a better understanding of nature's building blocks -- protons, neutrons and their constituent quarks -- as they are compressed inside the neutron star to a density trillions of times greater than on Earth.

Dr. Tod Strohmayer of NASA's Goddard Space Flight Center in Greenbelt, Md., and his colleague, Adam Villarreal, a graduate student at the University of Arizona, present these results today during a Web-based press conference in New Orleans at the meeting of the High Energy Astrophysics Division of the American Astronomical Society.

They said their best estimate of the radius of a neutron star is 7 miles (11.5 kilometers), plus or minus a stroll around the French Quarter. The mass appears to be 1.75 times that of the Sun, more massive than some theories predict. They made their measurements with NASA's Rossi X-ray Timing Explorer and archived X-ray data.

The long-sought mass-radius relation defines the neutron star's internal density and pressure relationship, the so-called equation of state. And this, in turn, determines what kind of matter can exist inside a neutron star. The contents offer a crucial test for theories describing the fundamental nature of matter and energy and the strength of nuclear interactions.

"We would really like to get our hands on the stuff at the center of a neutron star," said Strohmayer. "But since we can't do that, this is about the next best thing. A neutron star is a cosmic laboratory and provides the only opportunity to see the effects of matter compressed to such a degree."

A neutron star is the core remains of a star once bigger than the Sun. The interior contains matter under forces that perhaps existed at the moment of the Big Bang but which cannot be duplicated on Earth. The neutron star in today's announcement is part of a binary star system named EXO 0748-676, located in the constellation Volans, or Flying Fish, about 30,000 light-years away, visible in southern skies with a large backyard telescope.

In this system, gas from a "normal" companion star plunges onto the neutron star, attracted by gravity. This triggers thermonuclear explosions on the neutron star surface that illuminate the region. Such bursts often reveal the spin rate of the neutron star through a flickering in the X-ray light emitted, called a burst oscillation. (Refer to Items 1 - 6 for an artist's concept of this process. A movie and a detailed caption can be found in the blue column on the right.)

The scientists detected a 45-hertz burst oscillation frequency, which corresponds to a neutron star spin rate of 45 times per second. This is a leisurely pace for neutron stars, which are often seen spinning over 300 times per second.

The scientists next capitalized on EXO 0748-676 observations with the European Space Agency's XMM-Newton satellite from 2002, led by Dr. Jean Cottam of NASA Goddard. Cottam's team had detected spectral lines emitted by hot gas, similar in look to the lines of a cardiogram. These lines had two features. First, they were Doppler shifted. This means the energy detected was an average of the light spinning around the neutron star, moving away from us and then towards us. Second, the lines were gravitationally redshifted. This means that gravity pulled on the light as it tried to escape the region, stealing a bit of its energy.

Strohmayer and Villarreal determined that the 45-hertz frequency and the observed line widths from Doppler shifting are consistent with a neutron star radius between 9.5 and 15 kilometers, with the best estimate at 11.5 kilometers. The relationship among burst frequency, Doppler shifting and radius is that the velocity of gas swirling around the star's surface depends on the star's radius and its spin rate. In essence, a faster spin corresponds to a wider spectral line (a technique similar to how a state trooper can detect speeding cars).

Cottam team's gravitational redshift measurement offered the first measure of a mass-radius ratio, albeit without knowledge of a mass and radius. This is because the degree of redshifting (strength of gravity) depends on the mass and radius of the neutron star. Some scientists had questioned this measurement, for the spectral lines detected seemed too narrow. The new results strengthen the gravitational redshift interpretation of the Cottam team's spectral lines (and thus the mass-radius ratio) because a slower-spinning star can easily produce such relatively narrow lines.

So, ever more confident of the mass-radius ratio and now knowing the radius, the scientists could calculate the neutron star's mass. The value was between 1.5 and 2.3 solar masses, with the best estimate at 1.75 solar masses.

The result supports the theory that matter in the neutron star in EXO 0748-676 is packed so tightly that almost all protons and electrons are squeezed into neutrons, which swirl about as a superfluid, a liquid that flows without friction. Yet the matter isn't packed so tightly that quarks are liberated, a so-called quark star.

"Our results are really starting to put the squeeze on the neutron star equation of state," said Villareal. "It looks like equations of state which predict either very large or very small stars are nearly excluded. Perhaps more exciting is that we now have an observational technique that should allow us to measure the mass-radius relations in other neutron stars."

A proposed NASA mission called the Constellation X-ray Observatory would have the ability to make such measurements, but with much greater precision, for a number of neutron star systems.

Story Source:

The above story is based on materials provided by NASA/Goddard Space Flight Center. Note: Materials may be edited for content and length.

Cite This Page:

NASA/Goddard Space Flight Center. "Scientists Gain Glimpse Of Bizarre Matter In A Neutron Star." ScienceDaily. ScienceDaily, 21 September 2004. <www.sciencedaily.com/releases/2004/09/040921075823.htm>.
NASA/Goddard Space Flight Center. (2004, September 21). Scientists Gain Glimpse Of Bizarre Matter In A Neutron Star. ScienceDaily. Retrieved October 30, 2014 from www.sciencedaily.com/releases/2004/09/040921075823.htm
NASA/Goddard Space Flight Center. "Scientists Gain Glimpse Of Bizarre Matter In A Neutron Star." ScienceDaily. www.sciencedaily.com/releases/2004/09/040921075823.htm (accessed October 30, 2014).

Share This

More Space & Time News

Thursday, October 30, 2014

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Antares Liftoff Explosion

Raw: Antares Liftoff Explosion

AP (Oct. 29, 2014) Observers near Wallops Island recorded what they thought would be a routine rocket launch Tuesday night. What they recorded was a major rocket explosion shortly after lift off. (Oct 29) Video provided by AP
Powered by NewsLook.com
Raw: Russian Cargo Ship Docks at Space Station

Raw: Russian Cargo Ship Docks at Space Station

AP (Oct. 29, 2014) Just hours after an American cargo run to the International Space Station ended in flames, a Russian supply ship has arrived at the station with a load of fresh supplies. (Oct. 29) Video provided by AP
Powered by NewsLook.com
Journalist Captures Moment of Antares Rocket Explosion

Journalist Captures Moment of Antares Rocket Explosion

Reuters - US Online Video (Oct. 29, 2014) A space education journalist is among those who witness and record the explosion of an unmanned Antares rocket seconds after its launch. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com
Rocket Explosion Under Investigation

Rocket Explosion Under Investigation

AP (Oct. 28, 2014) NASA and Orbital Sciences officials say they are investigating the explosion of an unmanned commercial supply rocket bound for the International Space Station. It blew up moments after liftoff Tuesday evening over the launch site in Virginia. (Oct. 28) Video provided by AP
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.


Breaking News:

Strange & Offbeat Stories

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News


    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