Where All The Hottest Stars Gather

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An ESO telescope captures a group of hot young stars that would outshine any Hollywood party!

At the upper left of this image is the star cluster NGC 6604, a grouping of hot young stars within a larger collection located in the sky near the much more famous Eagle Nebula (of “Pillars of Creation” fame.) The young stars, which burn bright and blue, are helping make a new generation of stars with their strong stellar winds, which condense nearby gas and dust into even more star-forming regions.

Eventually the new stars will replace the ones seen here, which, although big and bright, will quickly burn through their stellar fuel and fade. Such is the life cycle of massive stars — live fast and die young.

This image was acquired by the MPG/ESO 2.2-meter telescope at the European Southern Observatory’s La Silla Observatory in Chile. NGC 6604 is about 5,500 light-years from Earth, located in the constellation Serpens. Read more on the ESO news release here.

NASA’s STEREO Spots a New Nova


While on duty observing the Sun from its position in solar orbit, NASA’s STEREO-B spacecraft captured the sudden appearance of a distant bright object. This flare-up turned out to be a nova — designated Sagittarii 2012 — the violent expulsion of material and radiation from a re-igniting white dwarf star.

Unlike a supernova, which is the cataclysmic collapse and explosion of a massive star whose core has finally fused its last, a nova is the result of material falling onto the surface of a white dwarf that’s part of a binary pair. The material, typically hydrogen and helium gas, is drawn off the white dwarf’s partner which has expanded into a red giant.

Eventually the white dwarf cannot contain all of the material that it has sucked in from its neighbor… material which has been heated to tremendous temperatures on its surface as it got compressed further and further by the white dwarf’s incredibly strong gravity. Fusion occurs on the dwarf’s outermost layers, blasting its surface out into space in an explosion of light and energy.

This is a nova — so called because, when witnessed in the night sky, one could suddenly appear as a “new star” in the heavens — sometimes even outshining all other visible stars!

An individual nova will soon fade, but a white dwarf can produce many such flares over time. It all depends on how rapidly it’s accreting material (and how much there is available.)

Over the course of 4 days, Sagittarii 2012 reached a magnitude of about 8.5… still too dim to be seen with the unaided eye, but STEREO-B was able to detect it with its SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) instrument, which is sensitive to extreme ultraviolet wavelengths.

The video above was made from images acquired from April 20 – 24, 2012.

It’s not known yet how far away Sagittarii 2012 is but rest assured it poses no threat to Earth. The energy expelled by a nova is nowhere near that of a supernova, and although you wouldn’t want to have a front-row seat to such an event we’re well away from the danger zone.

What this does show is that STEREO-B is not only a super Sun-watching sentinel, but also very good at observing much more distant stars as well!

Thanks to @SungrazerComets for the heads-up on this novel nova!

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Weekly SkyWatcher’s Forecast: April 9-15, 2012

[/caption]Greetings, fellow SkyWatchers! It’s shaping up to be a great week to enjoy astronomy. For both hemispheres, the Virginid Meteor shower is underway and its peak occurs late Monday night / early Tuesday morning. Need more celestial fireworks? Then keep looking up as the “April Fireballs” will be visiting, with their peak beginning about a week from today and lasting for 24 days. Even if you only catch one of these bright travelers as they sparkle across the starry sky, it will make your night! But hang on, there will be plenty to explore. Bright stars and bright planets are featured – as well as some of the season’s best galaxies. Keep your telescope out and don’t get spooked, because the “Ghost of Jupiter” will be a challenge object! If you want to know more about astonomy history, and what you can see with just your eyes and your optics, then meet me in the back yard…

Monday, April 9 – Tonight let’s take a journey towards the 25th brightest star in the night sky – 1.3 magnitude, Alpha Leonis. Regulus, known as “The Little King,” is the brightest star in Leo. At 77 light-years away, this star is considered a “dwarf” despite shining with a visible light almost 150 times that of Sol. The orange-red giant Arcturus and the blue white “dwarf” Regulus both share a common absolute magnitude very close to 0. The reason the two stars shine with a similar intrinsic brightness – despite widely different physical sizes – is Regulus’ photosphere is more than twice as hot (12,000 C) as Arcturus. While observing Regulus, look for a distant companion of magnitude 8.5. Normally low powers would best concentrate the companion’s light, but try a variety of magnifications to help improve contrast. For those with large aperture scopes, look for a 13.1 magnitude “companion’s companion” a little more than 2 arc seconds away!

Tuesday, April 10 – Be sure to get up before dawn to enjoy the Virginid meteor shower. The radiant point will be near Gamma in the bowl of Virgo. The fall rate of 20 per hour is above average for meteor showers, and with the Moon partially out of the equation this morning, you’re in for a treat!

Tonight, let’s have a look at Arcturus – a star whose distance from the Earth (10 parsecs) and radial velocity (less than 200 meters per second) can almost be considered a benchmark. By skydark you will see 0.2 magnitude, Arcturus – the brightest star in Bootes and 4th brightest star in the night sky – some 30 degrees above the eastern horizon. Apparent to the eye is Arcturus’ orange color. Because a star’s intrinsic luminosity relates to its apparent brightness and distance, Arcturus’ absolute magnitude is almost precisely the same as its apparent magnitude. Just because Arcturus’ radial velocity is nearly zero doesn’t mean it isn’t on the move relative to our Sun. Arcturus is now almost as close as it will ever get and its large proper motion – perpendicular to our line of sight – exceeds 125 kilometers per second. Every 100 years Arcturus moves almost 1 degree across the sky!

Since you’ve looked at a red star, why not look at a red planet before you call it a night? Mars is still making a wonderful apparition. Have you noticed it dimming even more? Right now it should be about magnitude -0.5. You may have noticed something else about Mars in the eyepiece, too… It’s getting smaller!

Wednesday, April 11 – Today is the birthday of William Wallace Campbell. Born in 1862, Campbell went on to become the leader of stellar motion and radial velocity studies. He was the director of Lick Observatory from 1901 to 1930, and also served as president of the University of California and the National Academy of Sciences. Also born on this day – but in 1901 – was Donald H. Menzel – assistant astronomer at Lick Observatory. Menzel became Director of Harvard Observatory, an expert on the Sun’s coronosphere and held a genuine belief in the extraterrestrial nature of UFOs. Today in 1960, the first radio search for extraterrestrial civilizations was started by Frank Drake (Project Ozma). In 1986, Halley’s Comet closed within 65 million kilometers of the Earth – as close as it would get.

Tonight, why don’t we honor Campbell’s work as we try taking a look at a variable ourselves? RT (star 48) Aurigae is a bright cephid that is located roughly halfway between Epsilon Geminorum and Theta Aurigae. This perfect example of a pulsating star follows a precise timetable of 3.728 days and fluxes by close to one magnitude.

Thursday, April 12 – Today in 1961, Yuri Gagarin made one full orbit of the Earth aboard Vostok 1, while also becoming the first human in space. Also today (in 1981) Columbia became the first Space Shuttle to launch.

Break out the telescope tonight and launch your way towards Iota Cancri – a fine wide disparate double of magnitudes 4.0 and 6.6 separated by some 30 arc seconds. This true binary is so distant from one another that they take over 60,000 years to complete a single orbit around their common center of gravity! Located slightly less than a fist’s width due north of M44, this pair is about 300 light years distant. Both stars shine with a light considerably brighter than our Sun and observers may note a subtle gold and pale blue color contrast between them.

Friday, April 13 – With no early evening Moon to contend with, this is a fine opportunity to have a look at a group of galaxies between Leo’s paws. Start at Regulus and look due east toward Iota Leonis. Halfway between the two (less than a fist from Regulus) and two finger-widths northeast of Rho Leonis, you’ll encounter Messier Galaxies M95 (Right Ascension: 10 : 44.0 – Declination: +11 : 42) and M96 (Right Ascension: 10 : 46.8 – Declination: +11 : 49) – both within the same low power field of view. At magnitude 9.2, the brighter – and slightly rounder – M96 lies northeast of 9.7 magnitude, M95. Pierre Mechain discovered both galaxies on March 20, 1781 and Messier added them to his catalog 4 days later. These two galaxies are two of the brightest members of the Leo I galaxy group located some 38 million light-years away.

To see another Messier member of the Leo I group, center on M96 and shift the galaxy south. From the north side of the low power field, the 9.3 magnitude galaxy M105 (Right Ascension: 10 : 47.8 – Declination: +12 : 35), nearby 10th magnitude NGC 3384 (Right Ascension: 10 : 48.3 – Declination: +12 : 38), and 12th magnitude NGC 3389 (Right Ascension: 10 : 48.5 – Declination: +12 : 32) will come into view. M105 was discovered by Mechain on the night Messier catalogued M95 and 96 but was not formally added to Messier’s catalog. Based on Mechain’s observing notes, Helen Sawyer Hogg added it to Messier’s list in 1947 – along with galaxy M106 and globular cluster M107. Mechain failed to notice M105’s bright neighboring galaxy – NGC 3384. NGC 3384 is actually slightly brighter than the faintest Messier discovered – M91.

We’re not done yet! If you center on M105 and shift due north less than a degree and a half you will encounter 10th magnitude NGC 3377 (Right Ascension: 10 : 47.7 – Declination: +13 : 59) – a small elongated galaxy with a stellar core. There are a dozen galaxies visible to moderate amateur instruments (through magnitude 12) in the Leo I region of the sky!

Saturday, April 14 – Today is the birthday of Christian Huygens. Born in 1629, the Dutch scientist went on to become one of the leaders in his field during the 17th century. Among his achievements were promoting the wave theory of light, patenting the pendulum clock, and improving the optics of telescopes by inventing a new type eyepiece and reducing false color through increasing the focal length of refractor telescopes. Huygens was the first to discover Saturn’s rings and largest satellite – Titan. Of the rings, Huygens said, “Saturn: encircled by a ring, thin and flat, nowhere touching, and inclined to the ecliptic.”

Wanna’ check Saturn out? It will be rising in the constellation of Virgo not long after the sky begins to turn dark. If you’re not sure of which “star” it is, just wait for awhile and you’ll find it about a fistwidth northwest of bright, blue/white Spica. Be sure to check out the ring system! Right now they have a very nice southern tilt which will allow you a great view of the shadow of the planet on the rings – and the shadow of the rings on the planet. If the atmosphere will allow, power up! Something you may never have thought of looking for could be happening… Can you see the planet’s edge through the Cassini division? Be sure to look for wide orbiting Titan and some of Saturn’s smaller moons slipping around the ring edges.

Tonight our challenge is also planetary – but it’s the planetary nebula – the “Ghost of Jupiter”. Begin by identifying the constellation of Hydra. Starting at Alpha Hydrae, head east about a fist’s width to find Lambda within a field of nearby fainter stars. Continue less than a fist southeast and locate Mu. You’ll find the “Ghost of Jupiter” (NGC 3242) lurking in the dark less than a finger-width due south. At magnitude 9, the NGC 3242 (Right Ascension: 10 : 24.8 – Declination: -18 : 38) gives a strikingly blue-green appearance in even small scopes – despite being more than 1500 light years away.

Sunday, April 15 – Tonight keep a watch for the “April Fireballs.” This unusual name has been given to what may be a branch of the complex Virginid stream which began earlier in the week. The absolute radiant of the stream is unclear, but most of its long tails will point back toward southeastern skies. These bright bolides can possibly arrive in a flurry – depending on how much Jupiter’s gravity has perturbed the meteoroid stream. Even if you only see one tonight, keep a watch in the days ahead. The time for “April Fireballs” lasts for two weeks. Just seeing one of these brilliant streaks will put a smile on your face!

And if you can’t take your eyes off Leo, then there’s good reason. The combination of Theta Leonis, Regulus and Mars certainly calls attention to itself!

While we’re out, let’s journey this evening towards another lovely multiple system as we explore Beta Monocerotis. Located about a fist width northwest of Sirius, Beta is one of the finest true triple systems for the small telescope. At low power, the 450 light year distant white primary will show the blue B and C stars to the southeast. If skies are stable, up the magnification to split the E/W oriented pair. All three stars are within a magnitude of each other and make Beta one of the finest sights for late winter skies.

If you hadn’t noticed, Saturn is at opposition tonight, meaning it will be viewable from dusk until dawn. Be sure to check out the “Ring King” – but wait until it has risen well above the lower atmosphere disturbance for a superior view!

Until next week, I wish you clear and steady skies!

Hubble Gets Best Look Yet At Messier 9

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First discovered by Charles Messier in 1764, the globular cluster Messier 9 is a vast swarm of ancient stars located 25,000 light-years away, close to the center of the galaxy. Too distant to be seen with the naked eye, the cluster’s innermost stars have never been individually resolved… until now.

This image from the Hubble Space Telescope is the most detailed view yet into Messier 9, capturing details of over 250,000 stars within it. Stars’ shape, size and color can be determined — giving astronomers more clues as to what the cluster’s stars are made of. (Download a large 10 mb JPEG file here.)

Hot blue stars as well as cooler red stars can be seen in Messier 9, along with more Sun-like yellow stars.

Unlike our Sun, however, Messier 9’s stars are nearly ten billion years old — twice the Sun’s age — and are made up of much less heavy elements.

Since heavy elements (such as carbon, oxygen and iron) are formed inside the cores of stars and dispersed into the galaxy when the stars eventually go supernova, stars that formed early on were birthed from clouds of material that weren’t yet rich in such elements.

Zoom into the Messier 9 cluster with a video from NASA and the European Space Agency below:

The Hubble Space Telescope is a project of international cooperation between ESA and NASA. See more at www.spacetelescope.org.

Image credit: NASA & ESA. Video: NASA, ESA, Digitized Sky Survey 2, N. Risinger (skysurvey.org)

What Are The Different Types of Stars?

A star is a star, right? Sure there are some difference in terms of color when you look up at the night sky. But they are all basically the same, big balls of gas burning up to billions of light years away, right?  Well, not exactly. In truth, stars are about as diverse as anything else in our Universe, falling into one of many different classifications based on its defining characteristics.

All in all, there are many different types of stars, ranging from tiny brown dwarfs to red and blue supergiants. There are even more bizarre kinds of stars, like neutron stars and Wolf-Rayet stars. And as our exploration of the Universe continues, we continue to learn things about stars that force us to expand on the way we think of them. Let’s take a look at all the different types of stars there are.

Protostar:

A protostar is what you have before a star forms. A protostar is a collection of gas that has collapsed down from a giant molecular cloud. The protostar phase of stellar evolution lasts about 100,000 years. Over time, gravity and pressure increase, forcing the protostar to collapse down. All of the energy release by the protostar comes only from the heating caused by the gravitational energy – nuclear fusion reactions haven’t started yet.

Size chart showing our Sun (far left) compared to larger stars. Credit: earthspacecircle.blogspot.ca
Size chart showing our Sun (far left) compared to larger stars. Credit: earthspacecircle.blogspot.ca

T Tauri Star:

A T Tauri star is stage in a star’s formation and evolution right before it becomes a main sequence star. This phase occurs at the end of the protostar phase, when the gravitational pressure holding the star together is the source of all its energy. T Tauri stars don’t have enough pressure and temperature at their cores to generate nuclear fusion, but they do resemble main sequence stars; they’re about the same temperature but brighter because they’re a larger. T Tauri stars can have large areas of sunspot coverage, and have intense X-ray flares and extremely powerful stellar winds. Stars will remain in the T Tauri stage for about 100 million years.

Main Sequence Star:

The majority of all stars in our galaxy, and even the Universe, are main sequence stars. Our Sun is a main sequence star, and so are our nearest neighbors, Sirius and Alpha Centauri A. Main sequence stars can vary in size, mass and brightness, but they’re all doing the same thing: converting hydrogen into helium in their cores, releasing a tremendous amount of energy.

A star in the main sequence is in a state of hydrostatic equilibrium. Gravity is pulling the star inward, and the light pressure from all the fusion reactions in the star are pushing outward. The inward and outward forces balance one another out, and the star maintains a spherical shape. Stars in the main sequence will have a size that depends on their mass, which defines the amount of gravity pulling them inward.

The lower mass limit for a main sequence star is about 0.08 times the mass of the Sun, or 80 times the mass of Jupiter. This is the minimum amount of gravitational pressure you need to ignite fusion in the core. Stars can theoretically grow to more than 100 times the mass of the Sun.

Red Giant Star:

When a star has consumed its stock of hydrogen in its core, fusion stops and the star no longer generates an outward pressure to counteract the inward pressure pulling it together. A shell of hydrogen around the core ignites continuing the life of the star, but causes it to increase in size dramatically. The aging star has become a red giant star, and can be 100 times larger than it was in its main sequence phase. When this hydrogen fuel is used up, further shells of helium and even heavier elements can be consumed in fusion reactions. The red giant phase of a star’s life will only last a few hundred million years before it runs out of fuel completely and becomes a white dwarf.

White Dwarf Star:

When a star has completely run out of hydrogen fuel in its core and it lacks the mass to force higher elements into fusion reaction, it becomes a white dwarf star. The outward light pressure from the fusion reaction stops and the star collapses inward under its own gravity. A white dwarf shines because it was a hot star once, but there’s no fusion reactions happening any more. A white dwarf will just cool down until it becomes the background temperature of the Universe. This process will take hundreds of billions of years, so no white dwarfs have actually cooled down that far yet.

Red Dwarf Star:

Red dwarf stars are the most common kind of stars in the Universe. These are main sequence stars but they have such low mass that they’re much cooler than stars like our Sun. They have another advantage. Red dwarf stars are able to keep the hydrogen fuel mixing into their core, and so they can conserve their fuel for much longer than other stars. Astronomers estimate that some red dwarf stars will burn for up to 10 trillion years. The smallest red dwarfs are 0.075 times the mass of the Sun, and they can have a mass of up to half of the Sun.

Neutron Stars:

If a star has between 1.35 and 2.1 times the mass of the Sun, it doesn’t form a white dwarf when it dies. Instead, the star dies in a catastrophic supernova explosion, and the remaining core becomes a neutron star. As its name implies, a neutron star is an exotic type of star that is composed entirely of neutrons. This is because the intense gravity of the neutron star crushes protons and electrons together to form neutrons. If stars are even more massive, they will become black holes instead of neutron stars after the supernova goes off.

Supergiant Stars:

The largest stars in the Universe are supergiant stars. These are monsters with dozens of times the mass of the Sun. Unlike a relatively stable star like the Sun, supergiants are consuming hydrogen fuel at an enormous rate and will consume all the fuel in their cores within just a few million years. Supergiant stars live fast and die young, detonating as supernovae; completely disintegrating themselves in the process.

As you can see, stars come in many sizes, colors and varieties. Knowing what accounts for this, and what their various life stages look like, are all important when it comes to understanding our Universe. It also helps when it comes to our ongoing efforts to explore our local stellar neighborhood, not to mention in the hunt for extra-terrestrial life!

We have written many articles about stars on Universe Today. Here’s What is the Biggest Star in the Universe?, What is a Binary Star?, Do Stars Move?, What are the Most Famous Stars?, What is the Brightest Star in the Sky, Past and Future?

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

M-Class Dwarfs Could Be Good For Life After All

The number of HabCat stars, as a function of distance. Image credit: Turnbull, Tarter. Click to enlarge
Scientists have been searching actively for signs of intelligent extraterrestrial civilizations for nearly half a century. Their main approach has been to point radio telescopes toward target stars and to “listen” for electronic transmissions from other worlds. A radio telescope is like a satellite TV dish – only bigger. Just as you can tune your TV to different frequencies, or channels, researchers can use the electronics attached to a radio telescope to monitor different frequencies at which they suspect ET may be transmitting signals out into the galaxy.

So far, no broadcasts have been received. But then, no one knows how many other civilizations with radio transmitters are out there – or, if they exist, where they are likely to be found. It’s only recently that the existence of planets around other stars has been confirmed, and because current planet-finding techniques are limited to detecting relatively large planets, we have yet to find the first Earth-like planet orbiting another star. Most planet hunters believe it’s only a matter of time before we find other Earths, but no one can yet make even a well-founded guess about how many terrestrial planets are in our galactic neighborhood.

With so little information to go on, it has been difficult for scientists involved in SETI (the search for extra-terrestrial intelligence) to decide how to focus their search. So they’ve have had to make some assumptions. One of those assumptions, which may seem a bit odd at first, is that humans are “normal.” That is to say that, because we know for certain that intelligent life evolved on our planet, it stands to reason that other stars like ours may have planets like ours orbiting them, on which other intelligent civilizations have emerged. Based on this terrestrial bias, SETI searches thus far have focused on stars like our sun.

“The observational SETI programs have traditionally confined themselves to looking at stars that are very similar to our own star,” says Jill Tarter, director of the SETI Institute’s Center for SETI Research in Mountain View, California. “Because, after all, that’s the one place where we know that life evolved on a planetary surface and produced a technology that might be detectable across interstellar distances.”

Astronomers classify stars according to their surface temperature. The sun is a G-class star. SETI searches to date have focused on G stars and stars that are either somewhat hotter than the sun (F stars) or somewhat cooler than the sun (K stars). That has yielded a catalog of about a quarter of a million target stars. According to conventional astronomical wisdom, stars hotter than F-class would burn out too quickly for intelligent life to develop on planets that orbit them. Historically, M-dwarf stars, which are dimmer than K stars, also have been dismissed as potential SETI targets.

The two major arguments against M dwarfs have been:

They’re too dim. M dwarfs put out so little solar radiation that a habitable planet would have to be very close-in. Farther-out planets would be frozen solid, too cold for life. A close-in planet would be tidally locked, though, always showing the same face to the star, as the moon does to Earth. The star-facing side would roast, while the opposite side would freeze. Not so good for having lots of liquid water around. And, says Tarter, “Liquid water is essential for life, at least for life as we know it.”

They’re too active. M dwarfs are known to have a lot of solar-flare activity. Solar flares produce UV-B radiation, which can destroy DNA, and X-rays, which in large doses are lethal. Presumably such radiation would be as harmful to extraterrestrial life as it is to life on Earth.

These arguments seem reasonable. But there’s a catch. Most of the stars in the galaxy – more than two-thirds of them – are M dwarfs. If M dwarfs can host habitable planets, those planets might well be home to intelligent species. With radio transmitters. So, as scientists have begun to learn more about other solar systems, and as computer models of solar-system formation have gotten more sophisticated, some SETI researchers have begun to question the assumptions that led them to reject M dwarfs as potential SETI targets.

For example, atmospheric modeling has shown that if a planet orbiting an M dwarf close in had a reasonably thick atmosphere, circulation would transfer the sun’s heat around the planet and even out the temperature worldwide.

“If you put a little bit of greenhouse gas into an atmosphere, the circulations can keep that atmosphere at a reasonable temperature and you can dissipate the heat from the star-facing side and bring it around to the farside. And, perhaps, end up with a habitable world,” says Tarter.

Scientists have also learned that most of an M dwarf’s hyperactivity occurs early in its life cycle, during the first billion years or so. After that, the star tends to settle down and burn quietly for many billions of years more. Once the fireworks end, life might be able to take hold.

The question of M-dwarf habitability is a critical one for Tarter. The SETI Institute is in the process of building a new radio telescope, the Allen Telescope Array. Comprised of 350 small antennas, the array will do double duty: it will be used by radio astronomers to survey the skies and it will search for radio transmissions from extraterrestrial civilizations.

“It’s an observatory that will simultaneously and continuously do traditional radio-astronomy observing and SETI observations,” says Tarter. “It’s the first telescope ever that’s being built to optimize both of those strategies.”

For the most part, traditional radio-astronomy research will determine where the telescope gets pointed; the SETI Institute will simply hitch a ride on the incoming signals. The array combines the signals from the many small antennas to make a large virtual antenna. By adjusting the electronics, researchers will be able to form as many as eight virtual antennas, each pointed at a different star.

That’s where the M-dwarf question comes into play. At the highest frequencies that the telescope can receive, the instrument can focus on only a tiny spot in the sky. For the SETI search to be as efficient as possible, wherever the telescope is pointed, the institute’s researchers want to have several target stars to set their sights on. If only F, G and K stars are considered, there aren’t enough stars to go around. But if M dwarfs are included as targets, the number of prospects could increase as much as ten-fold.

“To make the most progress and to do the fastest survey of the largest number of stars in the next decade or so,” Tarter says, “I want a huge catalog of target stars. I want millions of stars.”

There is no way to know for sure whether M dwarfs host habitable planets. But no one has yet found a habitable planet around any star other than the sun, and it’s unlikely that one will be discovered for many years to come. Technology capable of finding Earth-sized planets is still in the development stage.

To do their work, though, SETI researchers don’t need to know whether or not the stars they’re investigating actually have habitable planets. They simply need to know which stars have the potential to host habitable worlds. Any star with potential belongs on their list.

“It’s not the star that I’m interested in,” Tarter says. “It’s the techno-signature from the inhabitants on a planet around the star. I don’t ever have to see the star, as long as I know that it’s in that direction. I don’t ever have to see the planet. But if I can see their radio transmitter – bingo! – I’ve gotten there. I’ve found a habitable world.”

That’s why Tarter and her colleagues want to know whether or not to include M dwarfs on their target list. To help answer that question, Tarter convened a workshop in July of this year that brought together astronomers, planetary scientists, biologists, and even a few geologists, to explore whether it made sense to add M dwarfs to the catalog of SETI target stars. Although workshop participants did identify some areas that require further research, no insurmountable problems turned up. The group plans to publish its preliminary findings for scrutiny by the wider scientific community.

And that means that if we ever do receive a radio signal from an extraterrestrial civilization, the beings who sent it just might be residents of a solar system with a dim, red M dwarf at its center.

Original Source: NASA Astrobiology

Double Jets Around Exploded Star

The spectacular NASA’s Chandra X-ray Observatory image of Cassiopeia A released today has nearly 200 times more data than the “First Light” Chandra image of this object made five years ago. The new image reveals clues that the initial explosion was far more complicated than suspected.

“Although this young supernova remnant has been intensely studied for years, this deep observation is the most detailed ever made of the remains of an exploded star,” said Martin Laming of the Naval Research Laboratory in Washington, D.C. Laming is part of a team of scientists led by Una Hwang of the Goddard Space Flight Center in Greenbelt, Maryland. “It is a gold mine of data that astronomers will be panning through for years to come.”

The one-million-second observation of Cassiopeia A uncovered two large, opposed jet-like structures that extend to about 10 light years from the center of the remnant. Clouds of iron that have remained nearly pure for the approximately 340 years since the explosion were also detected.

“The presence of the bipolar jets suggests that jets could be more common in relatively normal supernova explosions than supposed,” said Hwang. A paper by Hwang, Laming and others on the Cassiopeia A observation will appear in an upcoming issue of The Astrophysical Journal Letters.

X-ray spectra show that the jets are rich in silicon atoms and relatively poor in iron atoms. In contrast, fingers of almost pure iron gas extend in a direction nearly perpendicular to the jets. This iron was produced in the central, hottest regions of the star. The high silicon and low iron abundances in the jets indicate that massive, matter-dominated jets were not the immediate cause of the explosion, as these should have carried out large quantities of iron from the central regions of the star.

A working hypothesis is that the explosion produced high-speed jets similar to those in hypernovae that produce gamma-ray bursts, but in this case, with much lower energies. The explosion also left a faint neutron star at the center of the remnant. Unlike the rapidly rotating neutron stars in the Crab Nebula and Vela supernova remnants that are surrounded by dynamic magnetized clouds of electrons, this neutron star is quiet and faint. Nor has pulsed radiation been detected from it. It may have a very strong magnetic field generated during the explosion that helped to accelerate the jets, and today resembles other strong-field neutron stars (a.k.a. “magnetars”) in lacking a wind nebula.

Chandra was launched aboard the Space Shuttle Columbia on July 23, 1999. Less than a month later, it was able to start taking science measurements along with its calibration data. The original Cassiopeia A observation was taken on August 19, 1999, and then released to the scientific community and the public one week later on August 26. At launch, Chandra’s original mission was intended to be five years. Having successfully completed that objective, NASA announced last August that the mission would be extended for another five years.

The data for this new Cas A image were obtained by Chandra’s Advanced CCD Imaging Spectrometer (ACIS) instrument during the first half of 2004. Due to its value to the astronomical community, this rich dataset was made available immediately to the public.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at:

http://chandra.harvard.edu
and
http://chandra.nasa.gov

Original Source: Chandra News Release