Fermi satellite detects gamma-rays from exploding novae

This picture is an artist's conception of the explosion of V407 Cygni. 

It shows the white dwarf exploding inside the outer layers of its nearby companion star. 

Credit: Photo by: David A. Hardy /astroart.org

The Universe is home to a variety of exotic objects and beautiful phenomena, some of which can generate almost inconceivable amounts of energy.

ASU Regents' Professor Sumner Starrfield is part of a team that used the Large Area Telescope (LAT) onboard NASA's Fermi Gamma-ray Space Telescope satellite to discover very high energy gamma rays (the most energetic form of light) being emitted by an exploding star.

Fermi Gamma-ray Space Telescope satellite

The surprising discovery dispels the long-held idea that classical nova explosions are not powerful enough to produce such high-energy radiation.

In March 2010, scientists using the LAT reported a surprising discovery: detection of gamma rays that appeared to come from a nova, V407 Cygni.

The LAT, in orbit around the Earth, views ∼20% of the sky instantaneously and the entire sky every three hours.

It is the most sensitive gamma-ray space telescope ever flown.

A nova is observed as a sudden, short-lived rapid increase in the brightness of an otherwise inconspicuous star.

It results from runaway thermonuclear explosions that typically take place in a binary system on the surface of a white dwarf fueled by mass from a companion star.

The outburst occurs when a white dwarf erupts in an enormous thermonuclear explosion.

The explosion is equivalent to about 100,000 times the energy that the sun gives off every year. Unlike supernovas, novae do not result in the destruction of their stars.

Although novae produce bright optical events, they had not previously been considered as potential sources of high energy gamma rays since they are not predicted to accelerate particles to the required energies (very nearly the speed of light).

Few cosmic marvels can accelerate particles to the energies required to generate gamma rays, billions of times more energetic than the type of light visible to our eyes.

Researchers had expected and seen X-rays from the resulting waves of expanding gas in prior novae.

The finding overturned the notion that novae explosions lack the power to emit such high-energy radiation.

Black Widow Pulsars With a deadly embrace - Video

Spinning 390 times a second, PSR J1311−3430 periodically swings its radio (green) and gamma-ray (magenta) beams past Earth in this artist's concept. 

The pulsar heats the facing side of its stellar partner to temperatures twice as hot as the sun's surface and slowly evaporates it. 

Credit: NASA's Goddard Space Flight Center

Black widow spiders and their Australian cousins, known as redbacks, are notorious for their tainted love, expressed as an unsettling tendency to kill and devour their male partners.

Astronomers have noted similar behaviour among two rare breeds of binary system that contain rapidly spinning neutron stars, also known as pulsars.

Roger Romani

"The essential features of black widow and redback binaries are that they place a normal but very low-mass star in close proximity to a millisecond pulsar, which has disastrous consequences for the star," said Roger Romani, a member of the Kavli Institute for Particle Astrophysics and Cosmology.

The Kavli institute is operated jointly by Stanford and SLAC National Accelerator Laboratory in Menlo Park, Calif.

Black widow systems contain stars that are both physically smaller and of much lower mass than those found in redbacks.

So far, astronomers have found at least 18 black widows and nine redbacks within the Milky Way, and additional members of each class have been discovered within the dense globular star clusters that orbit our galaxy.


Learn how astronomers discovered PSR J1311−3430, a record-breaking black widow binary and the first of its kind discovered solely through gamma-ray observations. 

Credit: NASA's Goddard Space Flight Center

One black widow system, named PSR J1311-3430 and discovered in 2012, sets the record for the tightest orbit of its class and contains one of the heaviest neutron stars known.

The pulsar's featherweight companion, which is only a dozen or so times the mass of Jupiter and just 60 percent of its size, completes an orbit every 93 minutes, less time than it takes to watch most movies.

Initial estimates put the neutron star at about 2.7 solar masses, but more recent studies allow a range of values extending down to 2 solar masses, still among the highest-known for neutron stars.

When a massive star explodes as a supernova, the crushed core it leaves behind – a neutron star—squeezes more mass than the sun into a ball no larger than Washington, D.C.

When young, an isolated neutron star rotates tens of times each second—or a few thousand revolutions per minute, and generates beams of radio, visible light, X-rays and gamma rays that astronomers observe as pulsed emission whenever the beams sweep past Earth.

They also generate powerful outflows, or "winds," of high-energy particles. The power for all this derives from the neutron star's rapidly spinning magnetic field, and over time, as solitary pulsars wind down, their emissions fade.

Thirty-two years ago, astronomers discovered a new, much faster class of pulsars. With rotation periods of 10 milliseconds or less, these neutron stars spin at astonishing speeds, up to 43,000 rpm.

Today, more than 300 of these so-called millisecond pulsars have been cataloged. While young pulsars usually appear in isolation, more than half of millisecond pulsars have a stellar partner, suggesting that interactions with a normal star can rejuvenate an older, slower neutron star.

But how did isolated millisecond pulsars get their groove back?

Enter black widows and their kin.

Read the full article here

NASA Kepler finds a very wobbly planet - Kepler-413b Binary System

This illustration shows the unusual orbit of planet Kepler-413b around a close pair of orange and red dwarf stars. 

The planet's 66-day orbit is tilted 2.5 degrees with respect to the plane of the binary star's orbit. 

The orbit of the planet wobbles around the central stars over 11 years, an effect called precession. 

This planet is also very unusual in that it can potentially precess wildly on its spin axis, much like a child's top. 

Credit: NASA, ESA, and A. Feild (STScI)

Imagine living on a planet with seasons so erratic you would hardly know whether to wear Bermuda shorts or a heavy overcoat.

That is the situation on a weird, wobbly world found by NASA's planet-hunting Kepler space telescope.

The planet, designated Kepler-413b, precesses, or wobbles, wildly on its spin axis, much like a child's top.

NASA's planet-hunting Kepler space telescope

The tilt of the planet's spin axis can vary by as much as 30 degrees over 11 years, leading to rapid and erratic changes in seasons.

In contrast, Earth's rotational precession is 23.5 degrees over 26,000 years.

Researchers are amazed that this far-off planet is precessing on a human timescale.

Precession : the axis of rotation of a precessing body itself rotates around another axis.

Kepler 413-b is located 2,300 light-years away in the constellation Cygnus. It circles a close pair of orange and red dwarf stars every 66 days.

Constellation Cygnus

The planet's orbit around the binary stars appears to wobble, too, because the plane of its orbit is tilted 2.5 degrees with respect to the plane of the star pair's orbit.

As seen from Earth, the wobbling orbit moves up and down continuously.

Kepler finds planets by noticing the dimming of a star or stars when a planet transits, or travels in front of them.

Normally, planets transit like clockwork. Astronomers using Kepler discovered the wobbling when they found an unusual pattern of transiting for Kepler-413b.

Veselin Kostov

"Looking at the Kepler data over the course of 1,500 days, we saw three transits in the first 180 days—one transit every 66 days—then we had 800 days with no transits at all. After that, we saw five more transits in a row," said Veselin Kostov, the principal investigator on the observation.

Kostov is affiliated with the Space Telescope Science Institute (STSCI) and Johns Hopkins University in Baltimore, Md.

The next transit visible from Earth's point of view is not predicted to occur until 2020.

This is because the orbit moves up and down, a result of the wobbling, in such a great degree that it sometimes does not transit the stars as viewed from Earth.

Astronomers are still trying to explain why this planet is out of alignment with its stars. There could be other planetary bodies in the system that tilted the orbit.

Or, it could be that a third star nearby that is a visual companion may actually be gravitationally bound to the system and exerting an influence.

Peter McCullough

"Presumably there are planets out there like this one that we're not seeing because we're in the unfavourable period," said Peter McCullough, a team member with the Space Telescope Science Institute (STSCI) and Johns Hopkins University.

"And that's one of the things that Veselin is researching: Is there a silent majority of things that we're not seeing?"

Even with its changing seasons, Kepler-413b is too warm for life as we know it.

Because it orbits so close to the stars, its temperatures are too high for liquid water to exist, making it inhabitable.

It also is a super Neptune—a giant gas planet with a mass about 65 times that of Earth—so there is no surface on which to stand.