Tag Archive for gas

Astronomers pinpoint launch of ‘bullets’ in a black hole’s jet

/ January 12, 2012 / No comments

ScienceDaily (Jan. 10, 2012) ? Using observations from NASA’s Rossi X-ray Timing Explorer (RXTE) satellite and the National Science Foundation’s (NSF) Very Long Baseline Array (VLBA) radio telescope, an international team of astronomers has identified the moment when a black hole in our galaxy launched super-fast knots of gas into space.

Racing outward at about one-quarter the speed of light, these “bullets” of ionized gas are thought to arise from a region located just outside the black hole’s event horizon, the point beyond which nothing can escape.

“Like a referee at a sports game, we essentially rewound the footage on the bullets’ progress, pinpointing when they were launched,” said Gregory Sivakoff of the University of Alberta in Canada. He presented the findings at the American Astronomical Society meeting in Austin, Texas. “With the unique capabilities of RXTE and the VLBA, we can associate their ejection with changes that likely signaled the start of the process.”

The research centered on the mid-2009 outburst of a binary system known as H1743-322, located about 28,000 light-years away toward the constellation Scorpius. Discovered by NASA’s HEAO-1 satellite in 1977, the system is composed of a normal star and a black hole of modest but unknown masses. Their orbit around each other is measured in days, which puts them so close together that the black hole pulls a continuous stream of matter from its stellar companion. The flowing gas forms a flattened accretion disk millions of miles across, several times wider than our sun, centered on the black hole. As matter swirls inward, it is compressed and heated to tens of millions of degrees, so hot that it emits X-rays.

Some of the infalling matter becomes re-directed out of the accretion disk as dual, oppositely directed jets. Most of the time, the jets consist of a steady flow of particles. Occasionally, though, they morph into more powerful outflows that hurl massive gas blobs at significant fractions of the speed of light.

In early June 2009, H1743-322 underwent this transition as astronomers watched with RXTE, the VLBA, the Very Large Array near Socorro, N.M., and the Australia Telescope Compact Array (ATCA) near Narrabri in New South Wales. The observatories captured changes in the system’s X-ray and radio emissions as the transformation occurred.

From May 28 to June 2, the system’s X-ray and radio emissions were fairly steady, although RXTE data show that cyclic X-ray variations, known as quasi-periodic oscillations or QPOs, gradually increased in frequency over the same period. On June 4, ATCA measurements showed that the radio emission had faded significantly.

Astronomers interpret QPOs as signals produced by the interaction of clumps of ionized gas in the accretion disk near the black hole. When RXTE next looked at the system on June 5, the QPOs were gone.

The same day, the radio emission increased. An extremely detailed VLBA image revealed a bright, radio-emitting bullet of gas moving outward from the system in the direction of one of the jets. On June 6, a second blob, moving away in the opposite direction, was seen.

Until now, astronomers had associated the onset of the radio outburst with the bullet ejection event. However, based on the VLBA data, the team calculated that the bullets were launched on June 3, about two days before the main radio flare. A paper on the findings will be published in the Monthly Notices of the Royal Astronomical Society.

“This research provides new clues about the conditions needed to initiate a jet and can guide our thinking about how it happens,” said Chris Done, an astrophysicist at the University of Durham, England, who was not involved in the study.

A super-sized version of the same phenomenon occurs at the center of an active galaxy, where a black hole weighing millions to billions of times our sun’s mass can drive outflows extending millions of light-years.

“Black hole jets in binary star systems act as fast-forwarded versions of their galactic-scale cousins, giving us insights into how they work and how their enormous energy output can influence the growth of galaxies and clusters of galaxies,” said lead researcher James Miller-Jones at the International Center for Radio Astronomy Research at Curtin University in Perth, Australia.

The Rossi X-ray Timing Explorer, which operated from Dec. 1995 to Jan. 2012, was managed by NASA’s Goddard Space Flight Center in Greenbelt, Md.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted from materials provided by NASA/Goddard Space Flight Center.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

Source: http://www.sciencedaily.com/releases/2012/01/120110173451.htm

tennis arcade fire brother mystique red faction what is my ip address nissan gtr

Category: advantage / Tags: , ,

Team of astronomers finds 18 new planets

/ December 4, 2011 / No comments

Friday, December 2, 2011

Discoveries of new planets just keep coming and coming. Take, for instance, the 18 recently found by a team of astronomers led by scientists at the California Institute of Technology (Caltech).

“It’s the largest single announcement of planets aside from the discoveries made by the Kepler mission,” says John Johnson, assistant professor of astronomy at Caltech and the first author on the team’s paper, which was published in the December issue of The Astrophysical Journal Supplement Series. The Kepler mission is a space telescope that has so far identified more than 1,200 possible planets, though the majority of those have not yet been confirmed.

Using the Keck Observatory in Hawaii?with follow-up observations using the McDonald and Fairborn Observatories in Texas and Arizona, respectively?the researchers surveyed about 300 stars. They focused on those dubbed “retired” A-type stars that are more than one and a half times more massive than the sun. These stars are just past the main stage of their life?hence, “retired”?and are now puffing up into what’s called a subgiant star.

To look for planets, the astronomers searched for stars of this type that wobble, which could be caused by the gravitational tug of an orbiting planet. By searching the wobbly stars’ spectra for Doppler shifts?the lengthening and contracting of wavelengths due to motion away from and toward the observer?the team found 18 planets with masses similar to Jupiter’s.

This new bounty marks a 50 percent increase in the number of known planets orbiting massive stars and, according to Johnson, provides an invaluable population of planetary systems for understanding how planets?and our own solar system?might form. The researchers say that the findings also lend further support to the theory that planets grow from seed particles that accumulate gas and dust in a disk surrounding a newborn star.

According to this theory, tiny particles start to clump together, eventually snowballing into a planet. If this is the true sequence of events, the characteristics of the resulting planetary system?such as the number and size of the planets, or their orbital shapes?will depend on the mass of the star. For instance, a more massive star would mean a bigger disk, which in turn would mean more material to produce a greater number of giant planets.

In another theory, planets form when large amounts of gas and dust in the disk spontaneously collapse into big, dense clumps that then become planets. But in this picture, it turns out that the mass of the star doesn’t affect the kinds of planets that are produced.

So far, as the number of discovered planets has grown, astronomers are finding that stellar mass does seem to be important in determining the prevalence of giant planets. The newly discovered planets further support this pattern?and are therefore consistent with the first theory, the one stating that planets are born from seed particles.

“It’s nice to see all these converging lines of evidence pointing toward one class of formation mechanisms,” Johnson says.

There’s another interesting twist, he adds: “Not only do we find Jupiter-like planets more frequently around massive stars, but we find them in wider orbits.” If you took a sample of 18 planets around sunlike stars, he explains, half of them would orbit close to their stars. But in the cases of the new planets, all are farther away, at least 0.7 astronomical units from their stars. (One astronomical unit, or AU, is the distance from Earth to the sun.)

In systems with sunlike stars, gas giants like Jupiter acquire close orbits when they migrate toward their stars. According to theories of planet formation, gas giants could only have formed far from their stars, where it’s cold enough for their constituent gases and ices to exist. So for gas giants to orbit nearer to their stars, certain gravitational interactions have to take place to pull these planets in. Then, some other mechanism?perhaps the star’s magnetic field?has to kick in to stop them from spiraling into a fiery death.

The question, Johnson says, is why this doesn’t seem to happen with so-called hot Jupiters orbiting massive stars, and whether that dearth is due to nature or nurture. In the nature explanation, Jupiter-like planets that orbit massive stars just wouldn’t ever migrate inward. In the nurture interpretation, the planets would move in, but there would be nothing to prevent them from plunging into their stars. Or perhaps the stars evolve and swell up, consuming their planets. Which is the case? According to Johnson, subgiants like the A stars they were looking at in this paper simply don’t expand enough to gobble up hot Jupiters. So unless A stars have some unique characteristic that would prevent them from stopping migrating planets?such as a lack of a magnetic field early in their lives?it looks like the nature explanation is the more plausible one.

The new batch of planets have yet another interesting pattern: their orbits are mainly circular, while planets around sunlike stars span a wide range of circular to elliptical paths. Johnson says he’s now trying to find an explanation.

For Johnson, these discoveries have been a long time coming. This latest find, for instance, comes from an astronomical survey that he started while a graduate student; because these planets have wide orbits, they can take a couple of years to make a single revolution, meaning that it can also take quite a few years before their stars’ periodic wobbles become apparent to an observer. Now, the discoveries are finally coming in. “I liken it to a garden?you plant the seeds and put a lot of work into it,” he says. “Then, a decade in, your garden is big and flourishing. That’s where I am right now. My garden is full of these big, bright, juicy tomatoes?these Jupiter-sized planets.”

###

California Institute of Technology: http://www.caltech.edu

Thanks to California Institute of Technology for this article.

This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.

This press release has been viewed 187 time(s).

Source: http://www.labspaces.net/115688/Team_of_astronomers_finds____new_planets

bradley cooper michael phelps un wall e sharon stone the girl with the dragon tattoo venus

Category: advantage / Tags: