Posts Tagged ‘pulsar’

Big Bang Monday: DNS Pulsar

Monday, May 4th, 2015

DNS in this case stands for “double neutron star” and a pulsar in the widest known orbit around another neutron star was discovered by two high school students.

In the summer of 2012, during a Pulsar Search Collaboratory workshop, two high-school students discovered J1930−1852, a pulsar in a double neutron star (DNS) system. Most DNS systems are characterized by short orbital periods, rapid spin periods and eccentric orbits. However, J1930−1852 has the longest spin period (Pspin∼185 ms) and orbital period (Pb∼45 days) yet measured among known, recycled pulsars in DNS systems, implying a shorter than average and/or inefficient recycling period before its companion went supernova. We measure the relativistic advance of periastron for J1930−1852, ω˙=0.00078(4) deg/yr, which implies a total mass (Mtot=2.59(4) M⊙) consistent with other DNS systems. The 2σ constraints on Mtot place limits on the pulsar and companion masses (mp1.30 M⊙ respectively). J1930−1852’s spin and orbital parameters challenge current DNS population models and make J1930−1852 an important system for further investigation.

A P–P˙ diagram showing all pulsars in DNS systems (stars/squares) and all other known pulsars (dots). Measured P and P˙ come from the ATNF Pulsar Catalog (Hobbs et al. 2004) and lines of characteristic age and surface magnetic field are shown with dot-dash and dashed lines, respectively. Recycled DNS pulsars (stars) appear between the normal and millisecond pulsar populations and are listed in Table 2. Despite its significantly longer spin period, J1930−1852 clearly belongs in the population of recycled DNS pulsars, unlike J1906+0746 and J0737−3039B (squares) – neither of which have undergone recycling.

With so many astronomers engaged in this type of work, it’s inspirational to find younger ones with no inhibitions and lots of hope continues to reap the rewards of discovery.




Big Bang Monday: Little Green Men

Monday, June 17th, 2013

Very interesting piece by Liz Fuller-Wright in the CSM last week on the discovery of variably-pulsating stars. Intially referred to as LGM-1 by the astronomers at the European Southern Observatory’s La Silla Observatory in Chile, including graduate student Jocelyn Bell. The “LGM” stood for “little green men.”

For seven years, the research team observed more than 3,000 young stars in the star cluster NGC 3766 for a few weeks each year. They found variable stars – 163 of them – including 36 that seem to break all the rules of pulsars. In fact, they held off on labeling the stars “pulsars,” choosing the less controversial label of “periodic variable stars,” though they said that they expect the scientific community to confirm that they are, in fact, pulsars.

As with many astronomic discoveries, it takes quite a while to confirm “discoveries.” This one in particular may rewrite the book on pulsar formation.

That’s pretty awesome. Maybe we’ll see pulsars in BigBangPrints soon.

Big Bang Monday: Super-energetic Millisecond Pulsar

Monday, November 7th, 2011

I like pulsars and I love how our friends at NASA GSFC explain it — with animation.

An international team of scientists using NASA’s Fermi Gamma-ray Space Telescope has discovered a surprisingly powerful millisecond pulsar that challenges existing theories about how these objects form.

At the same time, another team has located nine new gamma-ray pulsars in Fermi data, using improved analytical techniques.

A pulsar is a type of neutron star that emits electromagnetic energy at periodic intervals. A neutron star is the closest thing to a black hole that astronomers can observe directly, crushing half a million times more mass than Earth into a sphere no larger than a city. This matter is so compressed that even a teaspoonful weighs as much as Mount Everest.

“With this new batch of pulsars, Fermi now has detected more than 100, which is an exciting milestone when you consider that, before Fermi’s launch in 2008, only seven of them were known to emit gamma rays,” said Pablo Saz Parkinson, an astrophysicist at the Santa Cruz Institute for Particle Physics at the University of California Santa Cruz, and a co-author on two papers detailing the findings.

One group of pulsars combines incredible density with extreme rotation. The fastest of these so-called millisecond pulsars whirls at 43,000 revolutions per minute.

Millisecond pulsars are thought to achieve such speeds because they are gravitationally bound in binary systems with normal stars. During part of their stellar lives, gas flows from the normal star to the pulsar. Over time, the impact of this falling gas gradually spins up the pulsar’s rotation.

The strong magnetic fields and rapid rotation of pulsars cause them to emit powerful beams of energy, from radio waves to gamma rays. Because the star is transferring rotational energy to the pulsar, the pulsar’s spin slows after this transfer is completed.

Typically, millisecond pulsars are around a billion years old. However, in the Nov. 3 issue of Science, the Fermi team reveals a bright, energetic millisecond pulsar only 25 million years old.

The object, named PSR J1823−3021A, lies within NGC 6624, a spherical collection of ancient stars called a globular cluster, one of about 160 similar objects that orbit our galaxy. The cluster is about 10 billion years old and lies about 27,000 light-years away toward the constellation Sagittarius.

Fermi’s Large Area Telescope (LAT) showed that eleven globular clusters emit gamma rays, the cumulative emission of dozens of millisecond pulsars too faint for even Fermi to detect individually. But that’s not the case for NGC 6624.

“It’s amazing that all of the gamma rays we see from this cluster are coming from a single object. It must have formed recently based on how rapidly it’s emitting energy. It’s a bit like finding a screaming baby in a quiet retirement home,” said Paulo Freire, the study’s lead author, at the Max Planck Institute for Radio Astronomy in Bonn, Germany.

J1823−3021A was previously identified as a pulsar by its radio emission, yet of the nine new pulsars, none are millisecond pulsars, and only one was later found to emit radio waves.

Despite its sensitivity, Fermi’s LAT may detect only one gamma ray for every 100,000 rotations of some of these faint pulsars. Yet new analysis techniques applied to the precise position and arrival time of photons collected by the LAT since 2008 were able to identify them.

“We adapted methods originally devised for studying gravitational waves to the problem of finding gamma-ray pulsars, and we were quickly rewarded,” said Bruce Allen, director of the Max Planck Institute for Gravitational Physics in Hannover, Germany. Allen co-authored a paper on the discoveries that was published online today in The Astrophysical Journal.