Universe Today

XMM-Newton view of hot ionised gas halo in NGC 4631. Image credit: ESA Click to enlarge
Astronomers using ESA’s XMM-Newton observatory have found very hot gaseous haloes around a multitude of spiral galaxies similar to our Milky Way galaxy. These ‘ghost-like’ veils have been suspected for decades but remained elusive until now.

Galaxy ‘haloes’ are often seen in so-called ‘starburst’ galaxies, the locations of concentrated star formation, but the discovery of high-temperature haloes around non-starburst spiral galaxies opens the door to new types of measurements once only dreamed about.

For example, scientists can confirm models of galaxy evolution and infer the star-formation rate in galaxies like our own by ‘calculating backwards’ to estimate how many supernovae are needed to make the observed haloes.

“Most of these ghost-like haloes have never been confirmed before in X-ray energies because they are so tenuous and have a low-surface brightness,” said Ralph T?llmann, from the Ruhr University in Bochum, Germany, lead author of the results.

“We needed the high sensitivity and large light-collecting area of the XMM-Newton satellite to uncover these haloes.”

In starburst galaxies, which have prominent haloes, star formation and star death (supernovae) are concentrated in the core of the galaxy and occur during a short time period over the life of a galaxy. This intense activity forms a halo of gas around the entire galaxy, similar to a volcano sending out a plume.

So how can haloes form in the absence of intense star formation? T?llmann’s group say that the entire disk of a spiral galaxy can ‘simmer’ with star-formation activity. This is spread out over time and distance. Like a giant pot of boiling water, the steady activity of star formation over millions and millions of years percolates outward to form the galaxy halo.

Two of the best-studied galaxies so far out of a group of 32 are NGC 891 and NGC 4634, which are tens of millions of light years away in the constellations Andromeda and Coma Berenices, respectively.

The scientists noted that these observations do not support a recent model of galaxy halo formation, in which gas from the intergalactic medium rains down on the galaxy and forms the halo.

Galaxy halos contain about 10 million solar masses of gas. The scientists say it is a relatively straightforward calculation to determine how many supernovae are needed to create the halo. Supernovae are intricately tied to the rate of star formation in a given galaxy.

“With our data we will be able to establish for the first time a critical rate of star formation that needs to be exceeded in order to create such haloes,” said Dr Ralf-J?rgen Dettmar, a co-author also from Ruhr University.

Once these haloes have formed, the hot gas cools and can fall down onto the galaxy’s disk, the scientists said. The gas is involved in a new cycle of star formation, because pressure from this infalling gas triggers the collapse of gas clouds into new stars.

Some heavy elements might escape the halo into intergalactic space, depending on the energy of the supernovae. Further analysis of the chemical composition of the halo might reveal this.

This would determine the correctness of recent cosmological models on the evolution of galaxies, as well as provide evidence of how the elements necessary for life are distributed through the Universe.

Original Source: ESA Portal

A view of Buffy’s and other Kuiper belt object orbits. Image credit: CFHT Click to enlarge
A team of astronomers working in Canada, France and the United States have discovered an unusual small body orbiting the Sun beyond Neptune, in the region astronomers call the Kuiper belt. This new object is twice as far from the Sun as Neptune and is roughly half the size of Pluto. The body’s highly unusual orbit is difficult to explain using previous theories of the formation of the outer Solar System.

Currently 58 astronomical units from the Sun (1 astronomical unit, or AU, is the distance between the Earth and the Sun), the new object never approaches closer than 50 AU, because its orbit is close to circular. Almost all Kuiper belt objects discovered beyond Neptune are between 30 AU and 50 AU away. Beyond 50 AU, the main Kuiper belt appears to end, and what few objects have been discovered beyond this distance have all been on very high eccentricity (non-circular) orbits. Most of these high-eccentricity orbits are the result of Neptune “flinging” the object outward by a gravitational slingshot. However, because this new object does not approach closer than 50 AU, a different theory is needed to explain its orbit. Complicating the problem, the object’s orbit also has an extreme tilt, being inclined (tilted) at 47 degrees to the rest of the Solar System.

The Discovery and Follow-up

The object, which received the official designation 2004 XR 190 in the International Astronomical Union’s official announcement, was discovered during routine operation of the Canada-France Ecliptic Plane Survey (CFEPS) running as part of the Legacy Survey on the Canada France Hawaii Telescope. For now, the discoverers are using the temporary nickname “Buffy” to identify the new object, although they have proposed a different official name in keeping with normal procedures for naming such objects.

Buffy was extracted from the mountain of Legacy Survey data (about 50 gigabytes per hour of operation) by powerful computers combing through the telescopic images and producing hundreds of candidates. Astronomers then sift through the candidates to identify the distant comets.

Astronomer Lynne Allen of the University of British Columbia was the first to lay eyes on the new object, as she completed the initial identification in the course of processing CFEPS data from December 2004. “It was quite bright compared to the usual Kuiper belt objects we find”, said Dr. Allen, “but what was more interesting was how far away it was.”

The object’s brightness implies it is likely between 500 and 1000 kilometers (300 to 600 miles) in diameter. Buffy is thus a very large Kuiper belt object, but about half a dozen are larger.

“We immediately realized that the object was about twice as far as Neptune from the Sun and that its orbit was potentially nearly circular,” said UBC professor Brett Gladman, who noticed the unusual nature of the object when determining its orbit, “but further observations were required.”

One to two years of observations of a Kuiper belt object are required before their orbits can be precisely measured. The first additional observations of Buffy came in October 2005 when Gladman and Phil Nicholson of Cornell University used the Hale 5-meter telescope to re-observe the object.

Measurement of Buffy’s new position proved that the orbit was not only extremely tilted, inclined (tilted) at 47 degrees to the plane of the planetary system (essentially tying the record for a Kuiper belt object) but confirmed that Buffy was unlike any other previously-known object because it was on a nearly circular orbit while at a very large distance.

More measurements of Buffy’s position on images from telescopes at Kitt Peak National Observatories in Arizona by team members Joel Parker (Southwest Research Institute), as well as JJ Kavelaars (National Research Council of Canada, Herzberg Institute of Astrophysics) and Wes Fraser (University of Victoria), through November 2005 refined the estimate for Buffy’s closest approach to the Sun. Additional observations, to further confirm the orbit, where then provided by the CFHT Legacy Survey project. Astronomers will need to wait until February 2006 to measure the fine details of the Buffy’s orbit.

The team have reported their find to the Minor Planet Center, the clearinghouse for astronomical measurements of new minor planets. “To find the first known object with a nearly circular orbit beyond 50 AU is indeed intriguing,” reacted Brian Marsden, director of the MPC.

Challenging Theories

Although it is neither the smallest, largest, nor most distant object discovered in this region, the new Kuiper belt object has a highly unusual orbit which challenges theories of the evolution of the Solar System.

Why is Buffy’s orbit considered so unusual? Only one other detected object, Sedna, remains further than 50 astronomical units (AUs) from the Sun throughout its entire orbit. However, Sedna is on a very elliptical orbit, swooping in to 76 AU before traveling back out beyond 900 AU. In contrast, Buffy spends all of its time in the narrow range between 52 and 62 AU from the Sun. Combined with the tilt in its orbit, this new object challenges current theories about the history of the early Solar System.

Astronomers have detected other Kuiper belt objects that spend most of their time beyond 50 AU. These are on very elliptical orbits, and almost all approach within 38 AU of the Sun. That close approach places those objects within the reach of the gravitational influence of Neptune. These objects are generally thought to have been scattered out to their present orbits by a gravitational slingshot with Neptune. This group of objects was thus called the “Scattered Disk”.

Prior to the discovery of Buffy, a few other Kuiper belt objects were discovered which spend much of their time beyond 50 AU like those in the “Scattered Disk”, yet did not approach within the gravitational reach of Neptune. This group has been named the “Extended Scattered Disk”. Two of its members are 1995 TL8 and 2000 YW134, which approach to 40 AU of the Sun but have fairly elliptical orbits that take them back out beyond 60 AU. Two more extreme examples of the “Extended Scattered Disk” are 2000 CR105, which approaches to 44 AU, and Sedna, which never comes closer to the Sun than 76 AU.

Due to their large eccentricities, these objects are likely to have been strongly perturbed by something, although it could not have been Neptune because they do not come close enough to be scattered by that planet’s gravitational force. As both Sedna and 2000 CR105 also travel beyond 500 AU from the sun, one theory is that after being scattered by Neptune, a passing star could have pulled their closest approaches away from the Sun.

Buffy is clearly a member of the “Extended Scattered Disk”. However, Buffy’s almost circular orbit makes it stand out from the other members. In addition, Buffy’s large orbital tilt is not so easily explained by the passing star idea. If a star could have affected Buffy so strongly, it should also have disrupted much of the main Kuiper belt as well. Since astronomers do not detect that strong disruption, a more complex theory is needed to explain Buffy’s orbit.

The elusive explanation may lie in side-effects from rearrangements of the Solar System early in its history. One possibility is that as Neptune’s orbit slowly expanded in the young Solar System, complex gravitational interactions could have caused some Kuiper belt orbits to circularize and tilt. While Buffy’s orbit could have been created this way, this theory would not seem to explain 2000 CR105 and Sedna. This new discovery is exciting because it causes us to rethink our understanding of how the Kuiper belt formed.

The Future

Over the last half decade, theories about the formation of our outer Solar System have been pushed to their limits: unusual Kuiper belt objects, like Buffy, which never come close to Neptune yet have high inclination must be explained.

Although theories that explain individual objects exist, reproducing the entire ensemble of known objects with one process poses a difficult challenge to current solar system models. Because the unusual objects, like Buffy, are very rare, astronomers are still scratching the surface of the dark corners of the Kuiper belt. Future large-scale surveys that systematically explore the Kuiper belt are the only way unlock the mysteries of what happened early in the history of our Solar System.

Original Source: Canada-France-Hawaii Telescope

The new star cluster found by GLIMPSE. Image credit: NASA Click to enlarge
Astronomers have at last found inner light! Only, they didn’t find it through the typical Earthly methods of meditation, exercise and therapy. Instead, the light was discovered inside our Milky Way galaxy after hours of deep self-reflection with NASA’s Spitzer Space Telescope.

The astronomers, who are members of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) team, used Spitzer’s heat-seeking infrared eyes to gaze at the dust-drenched plane of our galaxy. When they did this, the galaxy’s obscuring clouds of gas and dust became transparent, revealing approximately 100 new star clusters, each containing tens to hundreds of stars.

According to lead investigator Emily Mercer, a graduate student at Boston University, Mass., the new clusters will tell astronomers a great deal about the structure of the Milky Way and star formation within the galaxy.

“These little guys were quite hard to find,” said Mercer. “The discovery required sophisticated computer sifting of GLIMPSE data and careful inspection of the Spitzer images.”

In the past, our galaxy wasn’t so quick to give up its stellar secrets. Because we sit inside its flat, spiral disk, most of the galaxy appears as a thick blurry band of light that stretches across the sky. Many of the stars in this galactic plane cannot be detected with visible-light or ultraviolet telescopes. That’s because the cool clouds of dust and gas that hover around the galaxy’s center and make up galactic spiral arms block their starlight from our view.

Two-thirds of the new star clusters were discovered through a computer method developed by Mercer and her advisor, Dr. Dan Clemens, also of Boston University. They used an algorithm to automatically sift through the GLIMPSE data for clusters. The rest were found using the traditional method of visually scrutinizing images for star clusters.

Mercer also found that there are nearly twice as many star clusters in the southern galactic plane, the portion of the galactic plane visible from the Earth’s southern hemisphere, as in the northern galactic plane. She suspects that this observation may help astronomers map the location of the Milky Way’s spiral arms.

“Emily has done a great job,” says Clemens. “Her computer method for finding clusters has proved to be the most successful automated effort to date.”

Both Clemens and Mercer are members of the multi-institutional GLIMPSE team, which is led by Dr. Edward Churchwell of the University of Wisconsin, Madison. The group was selected to survey the galactic plane with Spitzer’s infrared array camera in November 2000 as part of Spitzer’s Legacy program. So far, more than 30 million stars in the inner Milky Way have already been catalogued by GLIMPSE, and the team expects to identify more than 50 million stars by the end of the project.

“By making the galactic plane transparent, Spitzer opens a new door for astronomers to study the Milky Way,” says Churchwell. “Some of the most interesting science likely to come out of this project will be serendipitous discoveries, which will open up entirely new avenues of inquiry.”

Original Source: Spitzer Space Telescope