Universe Today

January 7, 2009December 24, 2015 by Ian O'Neill

WR 104 Won’t Kill Us After All

[/caption]Early last year, concern was growing for a Wolf-Rayet star named WR 104 that appeared to be aiming right at Earth (see Looking Down the Barrel of A Gamma Ray Burst). A Wolf-Rayet star is a highly unstable star coming to the end of its life, possibly culminating in a powerful, planet-killing gamma-ray burst (GRB). GRBs are collimated beams of high energy gamma-rays, projected from the poles of a collapsing Wolf-Rayet star. It was little wonder that we were concerned when a dying Wolf-Rayet star was found to be pointing right at us! Today, at the AAS in Long Beach, one scientist working at the Keck Telescope has taken a keen interest in WR 104 and shared new findings that show our Solar System may not be bathed in deadly gamma-rays after all…

Wolf-Rayet stars are evolved massive stars undergoing a suicidal and violent death. They are very hot (up to 50,000K) and losing mass very quickly, generating powerful stellar winds (at velocities of 2000 km/s). WR 104 was imaged using the Keck Telescope in Hawaii last March, and images of the pinwheel spiral star system appeared to show that we were “looking down a rifle barrel”.

So what is causing this spiral structure around WR 104? The star has a binary O-type star partner, so as WD 104 sheds its mass, the stellar winds spiral outward. As we are seeing the full spiral from Earth, it was therefore reasonable to assume the binary system was facing right toward us. As WR 104 probably has its pole pointing 90° from the ecliptic plane, any future GRB could be directed straight at us.

“WR 104 is a fascinating object that got a lot of press last spring,” Dr Grant Hill said during the AAS meeting today (Jan 7th). “Since the object is in our galaxy, it could be devastating [for Earth]”

Hill therefore decided to confirm previous Keck observations with spectroscopic data to find out if there could be the possibility of an Earth-directed GRB. His work confirms the system is a binary pair, orbiting each other at an 8 month period. Hill also confirmed the presence of a shock front between the stellar winds of WD 104 and O-type partner. And there is some very good news for Earth. It would appear the original Keck imagry may not have been as straight-forward as it seemed. Spectroscopic emission lines from the binary pair strongly suggest the system is in fact inclined 30°-40° (possibly as much as 45°) away from us.

So, Earth doesn’t appear to be in the firing line of WR 104 after all…

January 7, 2009December 24, 2015 by Fraser Cain

Atmospheres of Super Earths

Artist illustration of a super Earth around Gliese 581

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We stand on the edge of the next phase of planetary discovery. Hundreds of massive, Jupiter-like planets have been discovered, but now astronomers are turning up smaller, more familiar planets. Planets the mass of Earth are out of reach today, but a new class of super Earth planets are now being discovered, and more will be turned up with the next generation of ground and space-based telescopes. Perhaps the most interesting research will be in the atmospheres of these planets.

Super Earths can have up to 10 times the mass of the Earth, but with a solid surface and liquid water they could very well be habitable. A recent presentation by Eliza Miller-Ricci from Harvard University at the 213th meeting of the American Astronomical Society discussed the kinds of atmospheres astronomers might see as these super Earths start turning up. Although interesting scientifically – geologic outgassing, evidence of plate tectonics, and the thickness or thinness of the atmosphere, the most interesting question will be: can super Earth planets support life?

To have life as we understand it, super Earth planets (like regular Earth planets) will need to have liquid water on their surface, and the requires a certain temperature range – the parent star’s habitable zone. As we see in our own Solar System, the atmosphere of a planet helps regulate its temperature; Venus has a thick atmosphere and it’s hot enough to melt lead, while Earth has a nice temperature to allow liquid water to form on its surface. Mars has a thin atmosphere and it’s really cold. It’s not just the thickness of the atmosphere that matters, it’s also what’s in it: carbon dioxide, water, etc.

High mass planets like Jupiter are mostly formed from hydrogen. Low mass terrestrial planets like Earth can’t hold onto their hydrogen and it escapes into space during the planet’s early history. But these super Earths might be able to hold onto their hydrogen. Instead of a low-hydrogen atmosphere like Earth, they might have an atmosphere with large quantities of water. And water is a powerful greenhouse gas – trace amounts of water vapor in Earth’s atmosphere account for 60% of our greenhouse effect, keeping the planet warm and habitable.

I asked Miller-Ricci about what impact large quantities of hydrogen will have on the atmosphere of a super Earth planet. We have water here on Earth, but very little in the atmosphere. Water vapor is a powerful greenhouse gas and would help define the temperature of the planet. “The amount of hydrogen in the atmosphere of a super Earth planet would significantly affect its habitable zone. This is a really important question, it’s what we’re looking at next.”

Current missions can detect super Earths using the transit method, where the planet dims light from its parent star as it passes in front. By subtracting the chemical signature when the planet passes behind the star, astronomers can determine its atmosphere.

Finding super Earths is at the limit of current telescopes, but more powerful instruments are launching soon. NASA’s Kepler mission, launching in April 2009, will turn up even more super Earths than have already been found. But the next generation of space telescopes, like NASA’s James Webb Space Telescope will allow astronomers to image these planet’s atmospheres directly.

January 7, 2009December 24, 2015 by Nancy Atkinson

Invading Stars Faster Than Speeding Bullet

Bow shocks created by runaway stars. Credit: NASA/JPL/ESA

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A team of astronomers looking for pre-planetary nebulae using the Hubble Space Telescope instead came across some renegade stars screaming through space. These runaway stars are moving along at 50 km/s (112,000 miles an hour), and have traveled an estimated 160 light years from where they originated. “We think we have found a new class of bright, high-velocity stellar interlopers,” says astronomer Raghvendra Sahai from JPL. “Finding these stars is a complete surprise because we were not looking for them. When I first saw the images, I said ‘Wow. This is like a bullet speeding through the interstellar medium.’ Hubble’s sharp ‘eye’ reveals the structure and shape of these bow shocks.”

Just as a speedboat on a lake creates a wake, as these speedy stars plow through the interstellar “ocean” they create brilliant bow shocks as streams of matter flowing from the stars slam into the surrounding dense gas.

So far, 14 of these runaway stars have been found. What kind of stars are they? Astronomers can only estimate the ages, masses, and velocities of these renegade stars. The stars appear to be young — just millions of years old. Their ages are inferred from their strong stellar winds. Most star produce such winds either when they are very young or when they are dying, and Sahia said it is clear they are not dying. Massive dying stars produce flowing clouds of ionized gas around them and that type of gas is not around these interlopers and old stars are almost never found near dense interstellar clouds.

They appear to be medium-sized stars that are a few to eight times more massive than the sun.
The research team believes the interloper stars were dynamically ejected from their natal environments which were probably massive star clusters. There are two way this could have happened. One possible scenario is that a star in a binary system exploded as a supernova and the partner got kicked out. Another possibility is a collision between two binary star systems or a binary system and a third star. One or more of these stars could have picked up energy from the interaction and escaped the cluster.

Depending on their distance from Earth, the bullet-nosed bow shocks could be 100 billion to a trillion miles wide (the equivalent of 17 to 170 solar system diameters, measured out to Neptune’s orbit). The bow shocks indicate that the stars are traveling fast, more than 112,000 miles an hour (more than 180,000 kilometers an hour) with respect to the dense gas they are plowing through, which is roughly five times faster than typical young stars.

Runaway stars have been seen before. The Infrared Astronomical Satellite (IRAS), which performed an all-sky infrared survey in 1983, spied a few similar-looking objects. The first observation of these objects was in the late 1980s. But those stars produced much larger bow shocks than the stars in the Hubble study, suggesting that they are more massive stars with more powerful stellar winds.

“The stars in our study are likely the lower-mass and/or lower-speed counterparts to the massive stars with bow shocks detected by IRAS,” Sahai explains. “We think the massive runaway stars observed before were just the tip of the iceberg. The stars seen with Hubble may represent the bulk of the population, both because many more lower-mass stars inhabit the universe than higher-mass stars, and because a much larger number are subject to modest speed kicks.”

Astronomers have not spotted many of these stellar interlopers before because they are hard to find. “You don’t know where to look for them because you cannot predict where they will be,” Sahai says. “So all of them have been found serendipitously, including the 14 stars we found with Hubble.”

“One of the questions that these very showy encounters raise is what effect they have on the clouds,” says team member Mark Morris of the University of California, Los Angeles. “Is it an insignificant flash in the pan, or do the strong winds from these stars stir up the clouds and thereby slow down their evolution toward forming another generation of stars?”

Sahai and his team used Hubble’s Advanced Camera for Surveys to examine 35 objects that appeared as bright infrared sources in the IRAS archive. The team is planning follow-up studies to search for more interlopers, as well as study selected objects from this Hubble survey in greater detail in order to understand their effects on their environment.

Source: NASA, AAS Press Conference

January 7, 2009December 24, 2015 by Ian O'Neill

Could Quark Stars Explain Magnetars Strong Magnetic Field?

The magnetic field surrounding the mysterious magnetar (NASA)

[/caption]Magnetars are the violent, exotic cousins of the well known neutron star. They emit excessive amounts of gamma-rays, X-rays and possess a powerful magnetic field. Neutron stars also have very strong magnetic fields (although weak when compared with magnetars), conserving the magnetic field of the parent star before it exploded as a supernova. However, the huge magnetic field strength predicted from observations of magnetars is a mystery. Where do magnetars get their strong magnetic fields? According to new research, the answer could lie in the even more mysterious quark star…

It is well known that neutron stars have very strong magnetic fields. Neutron stars, born from supernovae, preserve the angular momentum and magnetism of the parent star. Therefore, neutron stars are extremely magnetic, often rapidly spinning bodies, ejecting powerful streams of radiation from their poles (seen from Earth as a pulsar should the collimated radiation sweep through our field of view). Sometimes, neutron stars don’t behave as they should, ejecting copious amounts of X-rays and gamma-rays, exhibiting a very powerful magnetic field. These strange, violent entities are known as magnetars. As they are a fairly recent discovery, scientists are working hard to understand what magnetars are and how they acquired their strong magnetic field.

Denis Leahy, from the University of Calgary, Canada, presented a study on magnetars at a January 6th session at this week’s AAS meeting in Long Beach, revealing the hypothetical “quark star” could explain what we are seeing. Quark stars are thought to be the next stage up from neutron stars; as gravitational forces overwhelm the structure of the neutron degenerate matter, quark matter (or strange matter) is the result. However, the formation of a quark star may have an important side effect. Colour ferromagnetism in color-flavour locking quark matter (the most dense form of quark matter) could be a viable mechanism for generating immensely powerful magnetic flux as observed in magnetars. Therefore, magnetars may be the consequence of very compressed quark matter.

These results were arrived at by computer simulation, how can we observe the effect of a quark star — or the “quark star phase” of a magnetar — in a supernova remnant? According to Leahy, the transition from neutron star to quark star could occur from days to thousands of years after the supernova event, depending on the conditions of the neutron star. And what would we see when this transition occurs? There should be a secondary flash of radiation from the neutron star after the supernova due to liberation of energy as the neutron structure collapses, possibly providing astronomers with an opportunity to “see” a magnetar being “switched on”. Leahy also calculates that 1-in-10 supernovae should produce a magnetar remnant, so we have a pretty good chance at spotting the mechanism in action.

January 7, 2009December 24, 2015 by Nancy Atkinson

This Week’s Where In The Universe Challenge

This week’s Where In The Universe Challenge has a new twist. This image was actually submitted by one of our readers, Wienie van der Oord from Israel. Its quite an interesting image, don’t you agree?! I’ll not give any hints as to where Wienie got the image, or what it is, or whether this image can be found anywhere else on the web (for those of you that like to search online for the image and link the answer!). You’ll have to wait until tomorrow (Thursday) for the answer to be revealed for this week’s Challenge. My only hope is that some conspiracy theorist types don’t see this and claim this image is proof of life on an alien world. Or, possibly, could it really be…..?!

Check back tomorrow to find out! It will be interesting to see the guesses on this one, so submit ’em in the comment section.

UPDATE (1/8): The answer has now been posted below. No peeking before you make your guess!

This image was certainly a lot of fun, and it’s one you can’t find anywhere else on the internet. It was sent in by UT reader Wienie van der Oord, and I’ll let her explain what it is:

“After a short rainfall in the Arava desert in Israel, a tiny desert plant developed a root and two leaves and looked like an “alien” running over another planet,” she said. The raindrops formed the “craters” in the desert sand, and the root going down into the ground suspended the seed above ground, making it look like this little bunny-like creature was scooting across an alien world. The plant in question that has just sprouted is the Zygophyllum Dumosum, a shrub native to Israel that can be found in the Judean desert and Dead Sea Valley, the Negev Hills and Arava Valley. Wienie sent another image too, after she scooped up the little “alien” and put it in her hand:

ZYGOPHYLLUM DUMOSUM sprout. Image credit: Wienie van der Oord

If you’re partial to plants, here’s a Wildflower of Israel website where you can find out more about this shrub.

Thanks to Wienie for sharing this very “cute” image. If you have an original photograph you’d like to submit or a suggested image for a Where In The Universe Challenge, you can send them to me. To find my email address you have to visit my personal website, nancyatkinson.com . Sorry, I’m not going to be spammed to death by posting my email address!

January 7, 2009December 24, 2015 by Tammy Plotner

Sagitta

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Sagitta belongs to the original 48 constellations charted by Ptolemy and it remains one of the 88 modern constellations defined by the International Astronomical Union. Located north of the ecliptic plane, it spans 80 square degrees of sky, ranking 86th in constellation size. Sagitta contains 4 main stars in its asterism and has 19 Bayer Flamsteed designated stars within its confines. It is bordered by the constellations of Vulpecula, Hercules, Aquila and Delphinus. Sagitta is visible to all observers located at latitudes between +90° and ?70° and is best seen at culmination during the month of August.

In ancient history, the constellation of Sagitta was once known as Sham – a name applied today to its Alpha star. It was the Romans who named it Sagitta, the “Arrow”. In ancient Greek myth, it depicted the weapon which Hercules used to kill the eagle Aquila – or perhaps the Stymphalian birds. Perhaps it is Cupid’s Arrow, or the one which the Centaur shot at Chiron… No matter which tale you choose, it’s unmistakeable arrow shape was clear to all cultures, including the Persians, Hebrews, Greeks and Romans. Only Johann Bayer seemed to have trouble with it… For it is one of those constellation in which he named the bright stars out of order!

Let’s begin our binocular tour of Sagitta with Alpha – the “a” symbol on our chart. While Sham isn’t the brightest star in the constellation, this yellow bright giant star’s name really does mean “arrow”. Located about about 475 light years from Earth, it has a stellar luminosity 340 times that of the Sun and is about 20 times larger. Sham falls inside the “Hertzsprung Gap,” a perimeter of stellar temperature and luminosity that few stars fit inside. From its point in stellar evolution, it should have stopped fusing hydrogen to helium and began to brighten. However, that’s not the case. For some reason, Sham’s surface shows an abundance of nitrogen – a state which could only occur from interior helium fusion. A Cepheid variable star in the making? Perhaps!

Take a look at Beta in binoculars – the “B” symbol on our map. It’s G-type yellow star like our own Sun. Beta Sagittae is a giant star and, like Sham, is only about 467 light years away from our solar system. Delta, in the center of the arrow, is a spectroscopic binary star. It consists of a class M giant star and a quiet little hydrogen fusing dwarf star. Both are happy at a distance of about 448 light years from here and both happily separated from each other by a little less than 9 AU. Don’t forget red giant star, Gamma, either! The “Y” star on our chart might be 275 light years away, but it shines 640 times brighter than our Sun! It, too, is highly evolved…. Surrounded by a shell and well on its way to becoming a Mira-type variable star and eventually a white dwarf star about the size of the Earth.

For large binoculars and small telescopes, set your sights towards Messier 71 (RA 19 : 53.8 Dec +18 : 47). At around 8th magnitude, this loosely structured globular cluster is a challenge for smaller optics, but a wonderful study. It was originally discovered by Philippe Loys de Chéseaux in 1746 and included by Charles Messier in his Messier catalog of comet-like objects in 1780. Residing about 12,000 light years away and spanning about 27 light years across, there has long been a debate about this star cluster’s proper designation… globular cluster or concentrated galactic star cluster? Thanks to modern photometry, astronomers have detected a short “horizontal branch” in the H-R diagram of M71, which is characteristic of a globular cluster. Its low metallicity content has now been recognized as that of a “youthful” globular cluster and its lack of RR Lyrae variables places it at an age of between 9 and 10 billion years old.

For two challenging large telescope studies, let’s try your hand with planetary nebulae. The first is NGC 6879 (RA 20 : 10.5 Dec +16 : 55). At an apparent magnitude of 13, this challenging study will require high magnification and careful alignment to pick out from the stellar field. However, don’t be discouraged, because the nebula itself is rather bright and conspicuous as a “hairy star”. Just as challenging is NGC 6886 (RA 20 : 12.7 Dec +19 : 59). While the central star is a magnitude brighter at 12, you’re going to need at least an 8″ telescope to detect this one. It has an unusual chemical composition which an OIII filter helps to reveal.

Sources:
Wikipedia
Chandra Observatory
SEDS
Chart Courtesy of Your Sky.

January 7, 2009April 26, 2016 by Fraser Cain

International Year of Astronomy Opening Ceremonies

George Hrab performing at the IYA 2009 Opening Ceremonies

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Nothing works better than repetition. 2009 is the International Year of Astronomy! We’ve said it more than a few times before, and you’ll read a lot of coverage over the next year here on Universe Today. But last night we got to officially kick things off and celebrate the beginning of IYA 2009 events in the US.

Chorus to the 365 Days of Astronomy podcast intro

The IYA 2009 opening ceremonies started out with a mini-concert by George Hrab. In addition to playing this gig, George provided the intro music for IYA 2009 365 Days of Astronomy podcast. The podcast has the chorus, but George has a longer version which he performed last night. George led a sing-along, performing the lyrics and the 700ish people in the audience helped out with the chorus. George is a great performer, and an amazing guy. Check out his podcast at http://www.geologicpodcast.com/

The highlight of the evening for me was a live linkup between the Los Angeles party and party goers at the Cincinnati Observatory. The live video worked out great, and there was a real feeling of camaraderie between the two locations. The big plan was for the Cincinnati folks to broadcast a live image of the Pleiades star cluster, but they had cloudy skies – a picture taken a few days ago was used instead.

There was a simultaneous ribbon cutting ceremony in Second Life, on the IYA 2009 island. Unfortunately, the island totally filled up, and it was difficult to actually interact with the people there. As we were singing along with George in the real world, the avatars in
Second Life were singing along too.

The final treat of the evening was a special advance viewing of the new PBS documentary, 400 Years of the Telescope, with a voiceover by Neil deGrasse Tyson. This documentary won’t air until April 12, 2009, sadly, so there’s no place to watch it until then. The documentary starts with the invention of the telescope and then follows the major technological improvements that bring us to the modern observatories we have today; and a peek a the supertelescopes coming down the road.

As we were walking out, Celestron had set up a constellation of telescopes to check out the night sky. Of course, Los Angeles doesn’t have the clearest skies. The Moon was up and we could just barely make out the stars in Orion. So people walking out from the ceremonies could get a chance to look at objects in the sky with their own eyes. In the middle of these expensive telescopes was the prototype for the Galileo Scope (more on this in another post), so we got to take it out for a test drive. I really want one. You know… for the kids.

If you want to watch it for yourself, the Astronomy Cast media team recorded the entire opening ceremonies – except for the PBS documentary. I have no idea how long it will still be available, but check it out here.

January 7, 2009December 24, 2015 by Tammy Plotner

Reticulum

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Located south of the ecliptic plane, the small, faint constellation of Reticulum was first named Rhombus by astronomical clock creator – Isaac Habrecht. It was later renamed Reticulum by Nicolas Louis de Lacaille in 1763. It spans 114 square degrees of sky, ranking 82nd in constellation size, has 4 main stars in its primary asterism and contains 11 Bayer Flamsteed designated stars within its confines. Reticulum is bordered by the constellations of Horologium, Dorado and Hydrus. It is visible to all observers located at latitudes between +23° and ?90° and is best seen at culmination during the month of January.

Since Reticulum is a “new” constellation, there is no mythology associated with it – only the story of how its name came to be. Originally named Rhombus by Isaac Habrecht, it was a name the fit the star pattern, considering a rhombus is a basic diamond pattern. Habrecht and his brother were talented Germany clock makers and one of their specialities was in fashioning astronomical clocks. As a matter of fact, they built the second astronomical clock in Strasbourg between 1571 and 1574. It was designed by mathematician Christian Herlin, and as well as the Habrecht brothers, had astronomer and musician David Wolckenstein to assist. This fantasy clock had a staircase, huge amounts of artwork, musical embellishments, but was best known for its complexity as an astronomical device. It had a calendar dial, the astrolabe, the indicators for planets and eclipses… and a celestial globe. When Lacaille made his sojourn to the Cape of Good Hope, his intent wasn’t to usurp Habrecht’s place in astronomical history – but to unify astronomical catalogs. In an attempt to honor instruments of science and his telescope for which he used to chart the southern skies, Lacaille named this trapezoidal collection of stars Reticulum, the Latin derivative for the reticule crosshairs on his spyglass which enabled him to accurately pinpoint star positions. The name Reticulum stuck and was later adopted as one of the 88 modern constellations by the International Astronomical Union.

Let’s begin our binocular tour of Reticulum with its brightest star – Alpha – the “a” symbol on our chart. Alpha Reticuli is a yellow G class giant star which is about 163 light years away from Earth. It shines about 237 times brighter than our Sun and is about 21 times larger. It will eventually end its life quietly as a white dwarf star. But, take out your telescope and have a closer look! You’ll find out that Alpha is also a binary star with a very disparate 12th magnitude companion star nearby. While the star hasn’t moved in the last 150 years, the pair does display the same proper motion.

Keep binoculars handy and hop west for Zeti Reticuli. This binary star system located about 39 light years away from our own solar system. The pair of twin suns are very much like our own in temperature and mass – yellow dwarf stars – but it’s there the similarities end. At one time, astronomers believed the Zeta pairing to be old galactic halo Population II subdwarf stars, but recent research indicates the may belong to the younger galactic disk population. This makes the twin Zetas far older than our Sun – in the neighborhood of 8 billion years old. And they aren’t moving along alone! The pair belongs to the Zeta Herculis Moving Star Group. Both stars share similar proper motions and distances – and despite being so widely spaced, they are a true binary star with an orbital period of an estimated million years!

While viewing Zeta, keep in mind all the legends behind this particular pair. In 1961, alien abductees – Barney and Betty Hill – were “taken” by citizens who imparted information to Betty that their home star was the Zeta system. After a map was constructed by an amateur astronomer and eventually debunked by Carl Sagan, then later sensationalized by Bob Lazar, the Zeta “planet” theory eventually went into hibernation for fear of media attention. On September 20, 1996 a tentative discovery of a “hot Jupiter” in the Zeta system was discovered and quickly retracted as being “pulsations” from the star… and while conditions are possible for Earth-like planets to exists around these twins suns, low solar metallicity makes their presence unlikely.

Before you give up planetary hopes, hop to Epsilon Reticuli – the backwards “3” symbol on our map. Now here’s a binary system located approximately 59 light-years away that really does have a confirmed planet! The primary star is an orange subgiant star, while the secondary star is a white dwarf star. As of 2000, an extrasolar planet has been confirmed to be orbiting the primary star in the system! It is roughly the size of Jupiter and it orbits around the star every 418 days. What’s more, there could possibly be an Earth-like trojan accompanying it!

For binoculars, keep a watch on R Reticuli – a Mira-type variable star. While it takes 278.3 days for it to go through it’s changes, they are very dramatic. You’ll find this incredible star begins by shining at respectable magnitude of 6.5 only to virtually turn telescopic at magnitude 14 during its minima. Now that’s variable!

For a small telescope and big binocular challenge, try your hand at NGC 1313 (RA 3 : 18.3 Dec -66 : 30). At magnitude 9 and more than 8 arc minutes in size, this starburst galaxy is often referred to as the “Topsy Turvy” because of its unusual supershell spiral galaxy structure. Located about 15 million light years away, large telescopes will pick out strange features, like spiral arms which are lopsided and its rotational axis is not at the center of the nuclear bar.

Now, have a go at NGC 1559 (RA 4 : 17.6 Dec -62 : 47). Although this barred spiral galaxy is over a magnitude fainter and about half the size of the last, you’ll still find it quite bright and rich in the telescope. Although it was originally thought to be a member of the Dorado Galaxy Group, this Seyfert Galaxy is all alone in space. NGC 1559 has massive spiral arms and strong star formation. It contains a small bar which is oriented nearly east-west and spans 40?. Its bar and galactic disc are the source of very strong radio emissions!

Our last galaxy is NGC 1543 (RA 4 : 12.8 Dec -57 : 44). Also about magnitude 10.5 and about 4 arc minutes in size, Dunlop 100 really is considered part of the Dorado Galaxy Group. Look for a very bright nucleus in this spiral galaxy, with a faint east to west extension!

Chart Courtesy of Your Sky.

January 7, 2009December 24, 2015 by Nancy Atkinson

Blogger Meet-Up Jan. 7 in Long Beach

The January AAS meeting is being held in Long Beach, CA (Image by Kevin Stanchfield)

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If you live near Long Beach or are there for the American Astronomical Society meeting, meet Fraser, Ian and the Astronomy Cast LIVE team at a “Blogger Meet-up” on Wed. January 7 at the Rock Bottom Brewery from 6pm – 9pm. The team hopes you can make it! (Have a tall cold one for me, OK?!)

And here’s the schedule for today’s press conferences, which will be streamed LIVE at Astronomy Cast LIVE’s UStream Channel: (all times Pacific Standard Time)

9:30 am: Black Holes
11:00 am: Ballistic Stellar Interlopers
12:30 pm: Extragalactic Background

Check it out!

January 6, 2009December 24, 2015 by Nancy Atkinson

With No Smoke or Mirrors, Spacecraft Hunts for Active Galaxies with Central Black Holes

Swift's Hard X-ray Survey offers the first unbiased census of active galactic nuclei in decades. Dense clouds of dust and gas, illustrated here, can obscure less energetic radiation from an active galaxy's central black hole. High-energy X-rays, however, easily pass through. Credit: ESA/NASA/AVO/Paolo Padovani

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NASA’s Swift spacecraft is designed to hunt for gamma-ray bursts. But in the time between these almost-daily cosmic explosions, Swift’s Burst Alert Telescope (BAT) scans the sky, performing an ongoing X-ray survey. Some of the first results of that survey were shared at the American Astronomical Society meeting in Long Beach, California. The BAT is revealing differences between nearby active galaxies and those located about halfway across the universe. Understanding these differences will help clarify the relationship between a galaxy and its central black hole. But unlike most telescopes, the BAT observations are not done with mirrors, optics or direct focusing. Instead, images are made by analyzing the shadows cast by 52,000 randomly placed lead tiles on 32,000 hard X-ray detectors. And BAT is becoming a workhorse: The survey is now the largest and most sensitive census of the high-energy X-ray sky.

“There’s a lot we don’t know about the workings of supermassive black holes,” says Richard Mushotzky of NASA’s Goddard Space Flight Center in Greenbelt, Md. Astronomers think the intense emission from the centers, or nuclei, of active galaxies arises near a central black hole containing more than a million times the sun’s mass. “Some of these feeding black holes are the most luminous objects in the universe. Yet we don’t know why the massive black hole in our own galaxy and similar objects are so dim.”

“The BAT sees about half of the entire sky every day,” Mushotzky said. “Now we have cumulative exposures for most of the sky that exceed 10 weeks.”

Galaxies that are actively forming stars have a distinctly bluish color (“new and blue”), while those not doing so appear quite red (“red and dead”). Nearly a decade ago, surveys with NASA’s Chandra X-Ray Observatory and ESA’s XMM-Newton showed that active galaxies some 7 billion light-years away were mostly massive “red and dead” galaxies in normal environments.

The BAT survey looks much closer to home, within about 600 million light-years. There, the colors of active galaxies fall midway between blue and red. Most are spiral and irregular galaxies of normal mass, and more than 30 percent are colliding. “This is roughly in line with theories that mergers shake up a galaxy and ‘feed the beast’ by allowing fresh gas to fall toward the black hole,” Mushotzky says.

Until the BAT survey, astronomers could never be sure they were seeing most of the active galactic nuclei. An active galaxy’s core is often obscured by thick clouds of dust and gas that block ultraviolet, optical and low-energy (“soft”) X-ray light. Dust near the central black hole may be visible in the infrared, but so are the galaxy’s star-formation regions. And seeing the black hole’s radiation through dust it has heated gives us a view that is one step removed from the central engine. “We’re often looking through a lot of junk,” Mushotzky says.

But “hard” X-rays — those with energies between 14,000 and 195,000 electron volts — can penetrate the galactic junk and allow a clear view. Dental X-rays work in this energy range.

Astronomers think that all big galaxies have a massive central black hole, but less than 10 percent of these are active today. Active galaxies are thought to be responsible for about 20 percent of all energy radiated over the life of the universe, and are thought to have had a strong influence on the way structure evolved in the cosmos.

The Swift spacecraft was launched in 2004.

Source: NASA