We'd like to welcome guest blogger Sebastian Heinz, Associate Professor in the Astronomy Department at the University of Wisconsin-Madison. He received his Ph.D. at the University of Colorado at Boulder. He studies relativistic jets -- a phenomenon observed around black holes and neutron stars, and began work on the project described here when he was a Chandra Postdoctoral Fellow at MIT.
Circinus X-1 had been a puzzle to X-ray astronomers almost from the moment of its discovery. It is an X-ray binary -- a neutron star sucking matter away from a companion star it is in orbit with, and it shines brightly when that matter spirals inward and eventually lands on the neutron star's surface. But it had defied classification into the basic categories scientists have been using for X-ray binaries. In some ways it behaves like a very young source, like the fact that the orbit of the two stars seems to change rapidly (and whenever things change rapidly in astronomy, we tend to infer that they cannot be very old). In other ways, it behaves like an old neutron star -- one that has lost most of the intense magnetic field which neutron stars are believed to be born with. It also blasts powerful streams of hot plasma, called jets, into interstellar space. And that's why I became interested. I study jets and I wanted to know why the jets from Circinus X-1 were able to light up and stay lit on scales of a few light years when other microquasar jets flared and then dimmed.
These two images from NASA's Chandra X-ray Observatory show a large change in X-ray brightness of a rapidly rotating neutron star, or pulsar, between 2006 and 2013. The neutron star - the extremely dense remnant left behind by a supernova - is in a tight orbit around a low mass star. This binary star system, IGR J18245-2452 (mouse over the image for its location) is a member of the globular cluster M28.
This graphic shows an exotic object in our galaxy called SGR 0418+5729 (SGR 0418 for short). As described in our press release, SGR 0418 is a magnetar, a type of neutron star that has a relatively slow spin rate and generates occasional large blasts of X-rays.
The only plausible source for the energy emitted in these outbursts is the magnetic energy stored in the star. 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 data shows that SGR 0418 doesn't fit that pattern. It has a surface magnetic field similar to that of mainstream neutron stars.
Note: An earlier version of this article appeared on this blog by Peter Edmonds.
The collapse of a massive star in a supernova explosion is an epic event. In less than a second a neutron star (or in some cases a black hole) is formed and the implosion is reversed, releasing prodigious amounts of light that can outshine billions of Suns. That is a spectacular way to be born. Here, I'll explain that the properties of neutron stars are no less spectacular, even though they are not as famous as their collapsed cousins, black holes.
Because of the incredible pressures involved in core collapse, the density of neutron stars is astounding: all of humanity could be squashed down to a sugar cube-sized piece of neutron star. The escape velocity from their surface is over half the speed of light but an approaching rocket ship would be stretched, then crushed and assimilated into the surface of the star in a moment. Resistance would be futile.
Neutron stars, the ultra-dense cores left behind after massive stars collapse, contain the densest matter known in the Universe outside of a black hole . New results from Chandra and other X-ray telescopes have provided one of the most reliable determinations yet of the relation between the radius of a neutron star and its mass. These results constrain how nuclear matter - protons and neutrons, and their constituent quarks, interact under the extreme conditions found in neutron stars.
It's a pleasure to welcome Martin Durant, of the University of Toronto, for a guest blog article giving more background about his work on the striking variations discovered in the Vela Pulsar.
Pulsars, the remnants of exploded massive stars, are fascinating objects. They have more mass than the sun, squeezed into a ball the size of a city, making them denser than the nucleus of an atom. Add to this mixture immense magnetic fields and rapid rotation, and you have the perfect mix of high energy particles and fundamental forces – nuclear, electromagnetic and gravitational – to put the extreme limits of physical models to the test. Each pulsar, when studied in sufficient detail, appears to be unique. To understand the differences between these exotic objects, we must use all available information and collect data across the spectrum, from radio to gamma rays.
The finite speed of light means that we must always be out of date, no matter how hard we strive to keep up with the times. The term look-back time refers to the time in the past when the light we now observe from a distant object was emitted. For example, deep Chandra observations have detected X-rays that have been travelling through intergalactic space for billions of years since they were emitted by jets of gas that were likely produced by rotating supermassive black holes. With these data, astronomers use Chandra and other telescopes as one-way time machines that enable them to see objects as they were in the past.
Observations with NASA's Chandra, Swift, and Rossi X-ray observatories, Fermi Gamma-ray Space Telescope, and ESA's XMM-Newton have revealed that a slowly rotating neutron star with a comparatively very weak surface magnetic field is giving off bursts of X-rays and gamma rays. This discovery may indicate the presence of an internal magnetic field much more intense than the surface magnetic field, with implications for how the most powerful magnets in the cosmos evolve.
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