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Dead Galaxies Make No Stars?

Whoa!  Not So Fast, Say Astronomers

For a long time, galaxies such as the elliptical galaxy M105, which lies about 40 million light-years away, were thought by astronomers to be “dead” — that is, lacking in the activities that lead to star formation. A new look at this old galaxy, done by University of Michigan astronomers, shows that it’s still creating stars. The discovery required that they look at the galaxy through ultraviolet-sensitive instruments to see the sites of starbirth (which glow brighter in UV).The galaxy isn’t flashy and bright like other, younger galaxies, but astronomers say that it’s still kicking out some newborn stars, albeit at a low level.

Galaxies generally come in two types: spiral galaxies, like our own Milky Way, and elliptical galaxies. The stars in spiral galaxies lie in a disk that also contains cold, dense gas, from which new stars are regularly formed at a rate of about one Sun per year.

Stars in elliptical galaxies, on the other hand, are nearly all billions of years old. These galaxies contain stars that orbit every which way, like bees around a beehive. Ellipticals have little, if any, cold gas, and no star formation was known.

According to University of Michigan research fellow Alyson Ford and astronomy professor Joel Bregman, astronomers really hadn’t seen much activity in older galaxies and assumed they stopped making stellar newborns long ago.  “Astronomers previously studied star formation by looking at all of the light from an elliptical galaxy at once, because we usually can’t see individual stars,” Ford said. “Our trick is to make sensitive ultraviolet images with the Hubble Space Telescope, which allows us to see individual stars.”

The technique enabled the astronomers to observe star formation, even if it is as little as one Sun every 100,000 years.

Ford and Bregman are working to understand the stellar birth rate and likelihood of stars forming in groups within ellipticals. In the Milky Way, stars usually form in associations containing from tens to 100,000 stars. In elliptical galaxies, conditions are different because there is no disk of cold material to form stars.

“We were confused by some of the colors of objects in our images until we realized that they must be star clusters, so most of the star formation happens in associations,” Ford said.

The team’s breakthrough came when they observed Messier 105, a normal elliptical galaxy that is 34 million light-years away, in the constellation Leo. Though there had been no previous indication of star formation in Messier 105, Ford and Bregman saw a few bright, very blue stars, resembling a single star 10 to 20 times the mass of the Sun.

They also saw objects that aren’t blue enough to be single stars, but instead are clusters of many stars. When accounting for these clusters, stars are forming in Messier 105 at an average rate of one Sun every 10,000 years, Ford and Bregman concluded. “This is not just a burst of star formation but a continuous process,” Ford said.

These findings bring about new mysteries to explore, such as the origin of the gas that forms the stars. “We’re at the beginning of a new line of research, which is very exciting, but at times confusing,” Bregman said. “We hope to follow up this discovery with new observations that will really give us insight into the process of star formation in these ‘dead’ galaxies.”</p>

The two collaborators present their findings today at a meeting of the Canadian Astronomical Society in London, Ontario.

Starbirth Beauty

Newborns Glitter in the Tarantula Nebula

Two new images — one from the NASA/ESA Hubble Space Telescope and the other from the European Southern Observatory’s Very Large Telescope — have produced given astronomers new insight into the processes of star formation. The first is an outstanding image that zeroes in on a section of the Tarantula Nebula, a vast star-forming cloud of gas and dust in the Large Magellanic Cloud. The view focuses on the central region of the nebula, where hot young stars are ionizing gases in the surrounding clouds.

The part of the nebula visible in this image from Hubble’s Advanced Camera for Surveys is criss-crossed with tendrils of dust and gas churned up by recent supernovae. These supernova remnants include NGC 2060, visible above and to the left of the center of this image, which contains the brightest known pulsar.

Not seen in this image are the remains of supernova SN 1987a — a stellar explosion that Hubble and other telescopes have been returning to spy on regularly since it blew up in 1987. Each subsequent visit shows an expanding shockwave lighting up the gas around the star, creating a pearl necklace of glowing pockets of gas around the remains of the star.

Together with dying stars, the Tarantula Nebula is packed with recently formed young stars have recently formed from the nebula’s supply of hydrogen gas. They shine with intense ultraviolet light that ionizes the gas, making it light up red. The light is so intense that from a distance of 170,000 light-years, the Tarantula Nebula is easily visible without a telescope on a dark night to Earth-bound observers.

A compact and extremely bright star cluster called RMC 136 lies above and to the left of this field of view, providing much of the radiation that powers the multi-colored glow. Until recently, astronomers debated whether the source of the intense light was a tightly bound cluster of stars, or perhaps an unknown type of super-star thousands of times bigger than the Sun. It is only in the last 20 years, with the fine detail revealed by Hubble and the latest generation of ground-based telescopes, that astronomers have been able to conclusively prove that it is, indeed, a star cluster.

But even if the Tarantula Nebula doesn’t contain this hypothetical super-star, it still hosts some extreme phenomena, making it a popular target for telescopes. Within the bright star cluster lies star RMC 136a1, which was recently found to be the heaviest ever discovered: the star’s mass when it was born was around 300 times that of the Sun. This heavyweight is challenging astronomers’ theories of star formation, smashing through the upper limit they thought existed on star mass.

The Drama of Starbirth

Astronomers using the European Southern Observatory’s Very Large Telescope have gotten a close-up view of just how newborn stars effect the gas and dust from which they formed. This view, of the star-forming region NGC 6729, is part of one of the closest stellar nurseries to Earth. This makes it one of the best-studied.

Stars form deep within molecular clouds and the earliest stages of their development cannot be seen through visible-light telescopes because of obscuration by dust. In this image, there are very young stars at the upper left of the picture. Although they cannot be seen directly, the havoc that they have wreaked on their surroundings dominates the picture. High-speed jets of material that travel away from the baby stars at velocities as high as one million kilometers per hour are slamming into the surrounding gas and creating shock waves. These shocks cause the gas to shine and create the strangely coloured glowing arcs and blobs known as Herbig–Haro objects.

In this view the Herbig–Haro objects form two lines marking out the probable directions of ejected material. One stretches from the upper left to the lower centre, ending in the bright, circular group of glowing blobs and arcs at the lower centre. The other starts near the left upper edge of the picture and extends towards the centre right. The peculiar scimitar-shaped bright feature at the upper left is probably mostly due to starlight being reflected from dust and is not a Herbig–Haro object. For more information, images, and a zoom-up video featuring this region, visit the ESO web site.

Also visit The Astronomer’s Universe here at Astrocast.TV for video explorations of starbirth and planetary formation. See my Star Birth video here.

Another Look at Star Birth and What Interests Astronomers

The Astronomer’s Universe with Carolyn Collins Petersen

Star Birth

Best seen Full Screen

This month another look at star birth from the viewpoint of what interests astronomers about this most fundamental process. The first stars came into existence just over 13 billion years ago and the procedures for making stellar objects have been occurring ever since then.  We see it happening in nearly every direction of the universe, in nearly every galaxy that exists.

You would think that such a ubiquitous process would be very well understood by astronomers. In very general terms, we do know the basic outlines of how it is that stars form from a nebula (a cloud of gas and dust) and ultimately end up as bright  self-luminous objects. But, as they always say, the devil is in the details.

What causes that cloud of gas and dust to start down the long road to star formation?  Why do some clouds produce huge numbers of clouds while others form just a few?  Where did the gases and dust in the star forming nebula come from?  What was the event that kicked off the formation of our own solar system?  What really happens in those very dense clouds of gas and dust that we can’t see into, such as those in the famous Pillars of Creation image from HST?

These questions and many others drive astronomers to study star birth regions in the Milky Way and beyond, using new technologies that allow them to peer beyond the clouds of gas and dust nearly to the hearts of stellar nurseries. It’s an exciting field of study that encompasses not just astronomy but astrophysics and chemistry (particularly the chemical interactions in the clouds where stars form).  The study of star birth ultimately also leads to the study of star death because for all the star forming regions we see today, stars had to die and contribute material in order for new generations of stars to form.  This is one of the many reasons that starbirth fascinates astronomers.

Re-post

Yale Astronomers Announce Birth of a Star

Birth of Star in Perseus ClusterAstronomers have long known that they are observing stars at different stages of their life cycle. Some stars are even observed in the years soon before they become an official star, that is, by having fusion take place in the core of the star. Now, by utilizing observations from the ground (Submillimeter Array in Hawaii) and in space (Spitzer Space Telescope), astronomers believe that they may be observing a star in the Perseus region of the sky, about 800 light years distant, immediately after it has begun its nuclear fusion in its core. Learn more about this discovery online now here.

Why Star Birth Fascinates Astronomers

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In the July segment of The Astronomer’s Universe, I explore the process of star birth from the viewpoint of what interests astronomers about this most fundamental process. The first stars came into existence just over 13 billion years ago and the procedures for making stellar objects have been occurring ever since then.  We see it happening in nearly every direction of the universe, in nearly every galaxy that exists.

You would think that such a ubiquitous process would be very well understood by astronomers. In very general terms, we do know the basic outlines of how it is that stars form from a nebula (a cloud of gas and dust) and ultimately end up as bright. self-luminous objects. But, as they always say, the devil is in the details.

What causes that cloud of gas and dust to start down the long road to star formation?  Why do some clouds produce huge numbers of clouds while others form just a few?  Where did the gases and dust in the star forming nebula come from?  What was the event that kicked off the formation of our own solar system?  What really happens in those very dense clouds of gas and dust that we can’t see into, such as those in the famous Pillars of Creation image from HST?

These questions and many others drive astronomers to study star birth regions in the Milky Way and beyond, using new technologies that allow them to peer beyond the clouds of gas and dust nearly to the hearts of stellar nurseries. It’s an exciting field of study that encompasses not just astronomy but astrophysics and chemistry (particularly the chemical interactions in the clouds where stars form).  The study of star birth ultimately also leads to the study of star death because for all the star forming regions we see today, stars had to die and contribute material in order for new generations of stars to form.  This is one of the many reasons that starbirth fascinates astronomers.

APEX Images Shock Wave Induced Stellar Births

The Atacama Pathfinder Experiment (APEX) telescope (sensitive in the submillimeter wavelengths of the electromagnetic spectrum) run by the European Southern Observatory (ESO) is located atop a 5000 meter high plateau in the Atacama desert of Chile. Yesterday the APEX team released an image of a region, over 4000 light years distant, of the constellation Scorpius within which there is an expanding cloud of gas which has apparently been responsible for the birth of newborn stars. This is in agreement with scientists’ current understanding of the life cycle of stars, often referred to as stellar evolution. To learn more go to http://www.eso.org/public/outreach/press-rel/pr-2008/pr-40-08.html

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