Posted on by Nancy Atkinson

25-Year Mystery of X-ray Emissions Solved

The plane of the Milky Way, recorded with the Chandra satellite in three colours: Photons with energies between 0.5 and 1keV appear red, those between 1 and 3keV green, and those between 3 and 7keV blue. Discrete sources are indicated by circles. Image: Mikhail Revnivtsev

[/caption]
25 years ago, astronomers discovered diffuse X-ray emissions coming from the plane of the Milky Way, but were puzzled by the source of those emissions. The mystery has now been solved by an international team of astronomers using the Chandra X-ray Observatory. These diffuse emissions do not originate from one single source but from white dwarf stars and stars with active outer gas layers.

Energetic X-ray emissions usually originate from very hot gases in a temperature range between 10 and 100 million degrees Celsius. And this so called “Galactic Ridge X-ray Emission” (GRXE) can also be found in very hot, optically thin plasma.

However, a gas with these thermal properties would immediately dissipate. Cosmic particles colliding with the interstellar medium could also be ruled out as an explanation for the GRXE.

Recently observations from two different satellites, the RXTE and Integral satellites, have shown that the X-ray emissions of the Milky Way exhibit the same distribution pattern as the stars. Since then, it has been assumed that a large portion of the GRXE originates from individual stars. These findings motivated the international team to carry out more precise measurements with the Chandra X-ray telescope.

The test area chosen was a small celestial region near the center of the Milky Way, and was about one and a half time the size of a full moon. Chandra identified 473 point sources of X-rays in a sector of the search field covering only 2.6 arcminutes. In a further step, the group used measurements from the Spitzer space telescope to prove that the results of the sector observed could be applied to the whole galaxy.

Most of the 473 X-ray sources are likely white dwarfs, which accrete matter from their surroundings. The sources could also be stars that have high activity in their outermost gas layer, the corona. White dwarfs are the remnants of extinct, low-mass suns. These cooling dead stars frequently orbit a partner, and in such a binary star system the white dwarf extracts matter from its larger partner until it becomes a Type Ia supernova.

The resolution of the diffuse X-ray emissions in our galaxy into discrete sources has far-reaching consequences for our understanding of a number of astrophysical phenomena. Astronomers can use the GRXE as a calibration for the spatial distribution of star populations within the Milky Way, for example. The results are also relevant for research into other galaxies, to determine if diffuse X-ray radiation from these objects also originates from white dwarfs and active stars.

The work was done by Mikhail Revnivtsev from the Excellence Cluster Universe at the TU Munich and his colleagues at the Max Planck Institute for Astrophysics in Garching, the Space Research Institute in Moscow and the Harvard-Smithsonian Center for Astrophysics in Cambridge, and was published in the April 30, 2009 edition of Nature.

Source: Max Planck Institute

Posted on by Nancy Atkinson

Obama to Re-examine Constellation Program

The Constellation program's Ares rockets. Credit: NASA

[/caption]
The White House is expected to announce on Thursday that they will order a full review of the NASA’s Constellation program. The reason for the review is to determine whether the Ares I rocket and the Orion crew capsule are the best options for replacing the space shuttle. According to the Orlando Sentinel, this announcement will coincide with the release of the Obama administration’s $18.7 billion spending plan for NASA. Obama has said little about NASA since he took office in January, but altering plans for the next generation of crewed space vehicles would be a major change of course for the space agency.

This review follows decisions by NASA to alter the Orion spacecraft – decreasing the crew size from six to four in order to save weight – as well as months of critical reports questioning whether the new Ares I rocket and Orion capsule will be ready to fly to orbit by 2015.

Other problems with Ares have surfaced, such as potential violent shaking caused by vibrations in its solid-rocket first stage, and the rocket’s tendency to drift on takeoff into its launch tower. Also, its estimate costs through 2015 have risen from $28 billion in 2006 to $44 billion today.

Agency and industry insiders said this budget proposal should offer the first major clues as to the new president’s plans for the agency, the Sentinel reported. Without an administrator NASA has not had clear direction from the current administration.

The news of a possible review of Constellation have given hope to the proponents of an alternative rocket system called Direct 2.0. The Direct system proposes a Jupiter 120 rocket, which is essentially the shuttle’s fuel tank and two solid rocket boosters with a capsule mounted on top in place of a side-mounted orbiter.

This plan was designed in part by NASA engineers working on their own time who were frustrated with the Ares rocket.

One study, called the Exploration Systems Architecture Study, or ESAS, ruled out using the military rockets and other systems while another independent study commissioned by NASA found that rockets currently being used by the military to launch top-secret spy satellites could be affordably and safely adapted to ferry humans to the international space station and, eventually, the moon and beyond.

But under administrator Mike Griffin, NASA decided against that course of action. The ESAS study was protested by many as having little input and participation from contractors and rocket companies.

Source: Orlando Sentinel

Posted on by Tammy Plotner

IYA Live Telescope Today – 30 Doradus: “The Tarantula Nebula”

Wow… If you had a chance to watch our live remote telescope today, then you were in for an awesome view of the Tarantula Nebula! Although it didn’t last very long before the dew and clouds chased us out, we were still able to take some great images and run some video footage for you to enjoy. Are you ready to have a look? Then step inside the library and brush away the cobwebs…

The Tarantula Nebula (also known as 30 Doradus, or NGC 2070) is an H II region in the Large Magellanic Cloud. It was originally thought to be a star, but in 1751 Nicolas Louis de Lacaille recognized its nebular nature.

The Tarantula Nebula has an apparent magnitude of 8. Considering its distance of about 180,000 light years, this is an extremely luminous non-stellar object. Its luminosity is so great that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in the Local Group of galaxies. It is also the largest and most active such region in the Local Group with an estimated diameter of 200 pc. The nebula resides on the leading edge of the LMC, where ram pressure stripping, and the compression of the interstellar medium likely resulting from this, is at a maximum. At its core lies the extremely compact cluster of stars (~2.5 pc diameter) – R136a – that produces most of the energy that makes the nebula visible.

The closest supernova since the invention of the telescope, Supernova 1987A, occurred in the outskirts of the Tarantula Nebula.

As always, you can visit the remote telescope by clicking on the IYA “LIVE Remote Cam” Logo to your right. Just remember if you get an error message, that means it is either daylight or cloudy. We’ll be broadcasting whenever skies are clear and dark in Central Victoria! Enjoy…

Factual information is copied from Wikipedia. Thank you so much!

Posted on by Tammy Plotner

A Twinkle in the Wolf’s Eye – IC 4406: A Hubble Visualization by Jukka Metsavainio

IC 4405 Parallel by JP Metsavainio

[/caption]

During the month of May, the “Wolf” rises and prowls the skies after midnight. Lupus was one of the 48 original constellations listed by the first century astronomer Ptolemy and on its western border is a Wolf-Rayet planetary nebula – IC 4406 – which contains some of the hottest stars known to be in existence. What exactly lay inside this 1900 light year distant torus-shaped cloud of dust? Then let’s really step inside this Hubble dimensional visualization by Jukka Metsavanio and take a closer look…

Whenever we present a dimensional visualization it is done in two fashions. The first is called “Parallel Vision” and it is much like a magic eye puzzle. When you open the full size image and your eyes are the correct distance from the screen, the images will seem to merge and create a 3D effect. However, for some folks, this doesn’t work well – so Jukka has also created the “Cross Version”, where you simply cross your eyes and the images will merge, creating a central image which appears 3D. As we learned some time ago, it might not always work for all people, but there are a few other tricks you can try. Now sit back and prepare to be blown away…

IC 4406 Cross by JP Metsavainio
IC 4406 Cross by JP Metsavainio

The rectangluar appearance of planetary nebula, IC 4406, isn’t such a great mystery. We know from looking at a great number of objects that our point of view affects how we see things and we realize we’re seeing this incredible structure almost in the plane of its equator. Astronomers believe the entirety of the nebula is shaped like a prolate spheroid – where the polar diameter is greater than the equatorial diameter. Why such an unusual shape? Quite probably because IC 4406 is believed to be bipolar. No. It’s not going to freak out on you… It simply means this planetary nebula has an axially symmetric bi-lobed appearance. This may be the beginnings or the endings of the evolutionary stages of all planetary nebulae – but it does have its quirks.

While the function that shapes this structure isn’t exactly clear to astronomers, many believe it may belong to the physical process known as bipolar outflow – continuous highly energetic streams of gas emanating from the poles of a star. What types of stars? Again, it isn’t always clear. Bipolar outflow can occur with protostars where a dense, concentrated jet produces a supersonic shock fronts. More evolved young stars, such as T-Tauri types, also produce bow shocks visible at optical wavelengths that we refer to as Herbig-Haro objects. Evolved stars produce spherically-symmetric winds (called post-AGB winds) that are focused into cones and eventually become classic planetary nebula structures. There is even speculation that these outflows may be impacting with interstellar dust surrounding the star or supernova remnants. But… what exactly causes these beautiful structures we see inside?

According to C.R. O’Dell: “This progression begins with dark tangential structures showing no alignment with the central star and location near the main ionization front. At the end of the progression in the largest nebulae, the knots are located throughout much of the ionized zone, where they are photoionized on the side facing the central star and accompanied by long tails well aligned radially. This modification of characteristics is what would be expected if the knots were formed near or outside the main ionization front, obtaining densities high enough to lead to their being only partially ionized as they are fully illuminated by the Lyman continuum (Lyc) radiation field. Their expansion velocities must be lower than that of the main body of the nebular shell. Their forms are altered by exposure to the radiation field from the star, although it is not clear as to the relative role of radiation pressure acting on the dust component vis-à-vis ionization shadowing.”

However, there is something a bit unusual about IC 4406, isn’t there? That’s right. It contains a Wolf-Rayet star. Descended from O-types, these massive, extremely luminous beauties have strong stellar winds and are well-known for spouting off their unprocessed outer H-rich layers. The dense, high-velocity winds then rip at the superheated stellar photosphere, unleashing ultra-violet radiation which in turn causes fluorescence in the line-forming wind region. Most continue on to become Ib or Ic type supernovae, and just a very few (only 10%) become the central stars of planetary nebulae. So is the beautiful patterns we see in IC 4406 the beginning or the end? Says C.R. O’Dell:

“We find knots in all of the objects, arguing that knots are common, simply not always observed because of distance. The knots appear to form early in the life cycle of the nebula, probably being formed by an instability mechanism operating at the nebula’s ionization front. As the front passes through the knots they are exposed to the photoionizing radiation field of the central star, causing them to be modified in their appearance. This would then explain as evolution the difference of appearance like the lacy filaments seen only in extinction in IC 4406… Theoretical models have considered only symmetric instabilities, but there seems to be nothing that precludes the formation of elongated concentrations like one sees in IC 4406.”

In the meantime, many of you will recognize these filaments in this planetary by its more common name – the “Retina Nebula” – the third to have its spatial distribution of H2 and CO emissions mapped to prove that the equatorial density is caused by the high-velocity outflow of the progenitor AGB star – and perhaps the twinkle in its eye could have either the beginnings or the end of what may have been planetary systems. Says R. Sahai: “It is suggested that the equatorial tori observed or deduced in IC 4406 results from ‘born again’ disks formed through the destruction of planetary systems at the end of the AGB evolutionary phase.”

Are these filaments shaped by magnetic fields? The work of Hanna Dahlgren opens some very interesting ideas: “We propose a theory where the magnetic fields control the sculpting and evolution of small-scale filaments. This theory demonstrates how the substructures may form magnetized flux ropes that are twisted around each other, in the shape of double helices. Similar structures, and with similar origin, are found in many other astrophysical environments.” And will they survive? Says C.R. O’Dell:

“What the future holds in store for the knots in PN is quite important because whichever mechanism is producing them is locking a substantial fraction of the mass into molecular knots and these knots are escaping from the gravitational field of the central star (Meaburn et al. 1998). The process of photoionization means that there will be photoevaporation of material from the knots. The situation will be very much like the proplyds in the Orion Nebula, where the inner molecular core is heated by photons of less than 13.6 eV, causing a slow flow of gas away from the core. When this gas reaches the knots’ ionization front it is photoionized and heated, then it is rapidly accelerated to a velocity of about 10 km s. The estimated evaporation timescale for the outward moving knots is several thousand years. Many or most of them will therefore survive the hot-luminous phase close to the star and will be ejected into the surrounding interstellar medium.”

As just another twinkle in the Wolf’s eyes…

Many thanks to JP Metsavainio of Northern Galactic for his magic with Hubble Space Telescope images and allowing us this incredible look inside another mystery of space.

Posted on by Nancy Atkinson

Alan Shepard, Freedom 7: May 5, 1961


48 years ago today, the US launched their first human to space. Alan Shepard flew on Mercury 3, a suborbital mission with a duration of only 15 minutes and 28 seconds. Shepard’s ship, Freedom 7, reached an altitude of 116.5 statute miles (186.4 km) and flew a distance of 303 statute miles (485 km). Enjoy this great video, which includes original footage, as well as Alan B Shephard talking about the flight. He also gives the real story about the “request to relieve himself” which was made famous in the movie “The Right Stuff.” Alan Shepard also flew on Apollo 14 (and made the famous golf shot on the moon.) He passed away in 1998.
Continue reading “Alan Shepard, Freedom 7: May 5, 1961”

Posted on by Nancy Atkinson

NASA Selects New Projects to Study Mars and Mercury

ExoMars Rover. Credit: ESA Click for larger version

[/caption]

Making good on its promise to work together with other space agencies, NASA has selected two science instruments that will fly on board European Space Agency (ESA) spacecraft, one heading to Mars on the ExoMars rover, the other to Mercury with the BepiColombo orbiter. “The selections will further advance our knowledge of these exciting terrestrial planets,” said Jim Green, director of NASA’s Planetary Division at NASA Headquarters in Washington. “The international collaboration will create a new chapter in planetary science and provide a strong partnership with the international science community to complement future robotic and human exploration activities.”

The Lander Radio-Science on ExoMars, or LaRa, will use NASA’s Deep Space Network of radio telescopes to track part of ESA’s ExoMars mission. Scheduled to launch in 2016, the mission consists of a fixed lander and a rover that will roam Mars collecting soil samples for detailed analysis.

Data relayed from the lander back to the network will allow scientists to measure and analyze variations in the length of the day and location of the planet’s rotational axis. This data will help researchers further dissect the structure of the Red Planet’s interior, including the size of its core. When combined with the lander’s onboard instruments, the data also may help confirm whether the planet’s interior is still, at least partially, composed of liquid. William Folkner of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., is the principal investigator. The project costs approximately $6.6 million.

BepiColombo - Mission to Mercury. Credit: ESA Click for larger version.
BepiColombo - Mission to Mercury. Credit: ESA Click for larger version.

The second science instrument selection, named Strofio, will employ a unique mass spectrometer on board the BepiColombo mission. The instrument will determine the mass of atoms and molecules to reveal the composition of Mercury’s atmosphere. The investigation will study the atmosphere, which is formed from material ejected from its surface, to reveal the composition of Mercury’s surface.

Strofio will be a component of the Italian Space Agency’s suite of science instruments that will fly aboard BepiColombo . Scheduled for launch in 2013, the mission is composed of two spacecraft. Japan will build one spacecraft to study the planet’s magnetic field. ESA will build the other to study Mercury directly. Stefano Livi of the Southwest Research Institute in San Antonio is the principal investigator. The project costs approximately $31.8 million.

The selections were chosen from eight proposals submitted in December 2008 in response to NASA’s new Stand Alone Mission of Opportunity, known as Salmon. NASA solicited proposals for investigations that address planetary science research objectives on non-agency missions. A key criterion is that science goals, including data archiving and analysis, must be accomplished for less than $35 million.

Source: NASA

Posted on by Nancy Atkinson

Hubble Servicing Mission Meets the Big Screen; Watch With Friends

Previous Hubble servicing mission. Credit: NASA

[/caption]
The crew of the upcoming Hubble servicing mission have not only been busy training for all contingencies of spaceflight on the shuttle and telescope repair (have you been following Astro_Mike on Twitter?) but they’ve also been training for the big screen. The REALLY big screen. NASA announced today that the crew will be using IMAX 3-D cameras to document this most complex of space shuttle operations — the final servicing mission to the Hubble Space Telescope. And in another bit of news, in a show of solidarity and support of the shuttle astronauts, astronomers from the University of Alabama are encouraging everyone to “raise a wing” to the Hubble repair crew.

The IMAX 3-D cameras will launch aboard space shuttle Atlantis, which is scheduled to lift off May 11. Astronauts will use the cameras to film five spacewalks needed to repair and upgrade Hubble. The IMAX footage will be combined with images from Hubble itself to create a new IMAX producton, “Hubble 3D,” set for release in spring 2010.

“We have worked with IMAX on past Hubble missions and are excited about working with them again on the current Hubble mission. The Hubble Space Telescope continues to dazzle us with the splendor of our universe, and after the mission we look forward to many more years of awe-inspiring imagery,” said Bob Jacobs, NASA’s acting assistant administrator for public affairs at NASA Headquarters in Washington. “IMAX has developed innovative 3-D image capture and projection technology that creates a large-scale, immersive educational experience in which those of us on the ground are no longer passive observers of spaceflight, we’re active participants.”

The IMAX team has trained Atlantis’ crew at NASA’s Johnson Space Center in Houston to operate the cameras. One will be mounted outside the crew cabin in the shuttle’s cargo bay to capture IMAX 3-D images of the historic final servicing mission. The commander and pilot will double as filmmakers as two teams of spacewalking astronauts — working in tandem with the shuttle’s robotic arm — perform some of the most challenging work ever undertaken in space as they replace and refurbish many of the telescope’s precision instruments.

And now for more on “raising a wing” to the crew, which came to us via Pamela Gay: Dr. William Keel of the University of Alabama Department of Physics and Astronomy is planning to head to the local Buffalo Wild Wings to watch NASA TV during the Hubble repair mission’s EVAs. This is perhaps astronomy’s “championship” event, and instead of the Final Four, it’s the final Hubble servicing mission. Keel will be watching with colleagues and students to take in the EVAs and perhaps even raise a Wild Wing in salute of the astronauts achievements.

On her Starstryder blog, Gay says, “While this idea started in Tuscaloosa, there is no reason for it to end there. Many restaurants and bars have cable television packages that include NASA TV. Next week, grab a friend and grab a beverage and ask the guy behind the bar to tune the TV into the greatest high risk game of all: It’s Man versus the Machine as Mike Massimino and the STS-125 team of astronauts upgrade the Hubble Space Telescope.”

If you’re interested in joining in, check out the NASA TV schedule.

Posted on by Nancy Atkinson

The Spitzer Space Telescope Speaks Its Mind

An interview with the Spitzer Space Telescope. Credit: NASA/JPL

[/caption]
The Spitzer Space Telescope is close to running out of coolant. Around May 12, the telescope will use up the last drop of the coolant that chills the instruments to just a few degrees above absolute zero. Everyone knew this was coming, but still it is sobering news. However, even though the coolant will be depleted, Spitzer will remain cold enough to still probe the universe with its infrared detectors for at least a couple of years. But we all like to think these missions will go on forever, at least I do anyway. The Jet Propulsion Laboratory shared this news in one of the more creative press releases ever put out by any NASA center: they interviewed the telescope. That’s right, the telescope. Not the principal investigator, not the chief engineer, but the telescope itself.

The spacecraft, which is now in orbit around the sun more than 100-million kilometers (62-million miles) behind Earth, will heat up just a bit — its instruments will warm up from – 456 degrees Fahrenheit (-271 Celsius) to – 404 degrees Fahrenheit (-242 Celsius).

If Spitzer could talk, here’s what the telescope might say:

Interviewer: It’s cold in here.

Spitzer: Sorry. Even though I’m warming up, I still need to be quite chilly for two of my infrared channels to continue working.

Interviewer: Why do infrared telescopes need to be cold?

Spitzer: Good question. Infrared light is produced by heat. So, engineers reduce my own heat to make sure that I’m measuring just the infrared light from the objects I’m studying. This is the same reason why I circle around the sun, far behind Earth, and why I have big sun shields — to keep cool.

Interviewer: Tell me, Spitzer, about what you consider to be your greatest discovery?

Spitzer: Probably my work on exoplanets, which are planets that orbit stars other than our sun. I hate to brag, but I was the first telescope to see actual light from an exoplanet. I was also the first to split that light up into a spectrum. Oh, sorry, there I go again with the techie talk. Light is made up of lots of different wavelengths in the same way that a rainbow is made up of different colors. I was able to split an exoplanet’s light up into its various infrared wavelengths. This spectral information teaches us about planets’ atmospheres.

Interviewer: What did you learn about the planets?

Spitzer: For one thing, I learned that the hot gas exoplanets, called “hot Jupiters,” are not all alike. Some are wild, with temperatures as hot as fire and almost as cold as ice. Others are more even-keeled. I also created the first temperature map of an exoplanet, and watched a storm of colossal proportions brewing across the face of one bizarre exoplanet – it has an orbit that swings in really close to its star and then back out to about where Earth sits in our solar system.

Interviewer: You seem to really like planets.

Spitzer: Well, you know, I wasn’t even originally designed to see exoplanets! It was a complete surprise to me that I had this amazing ability. I can tell you that I do, and always will, have a thing for planetary disks. Because I have infrared eyes, I can see the warm and dusty planetary materials that swirl in disks around young stars. I can also see older disks littered with the remnants of planets. In fact, I’ve probably looked at thousands of disks so far. What’s been fun is finding them around all sorts of oddball stars, such as those that are dead, doubled up as twins and even as small as planets. Bottom line is that the process of growing planets seems to happen quite easily all over the galaxy, and perhaps the universe.

Interviewer: Does that mean aliens could be everywhere?

Spitzer: I can’t really give you a good answer for that. Yes, the studies of disks are showing us that rocky planets are common, but we don’t know if the planets could have life. Also, keep in mind that, as of now, nobody has detected any planets that are just like Earth. These would be rocky worlds around stars like our sun that have the right temperature for lakes and oceans. That job will most likely fall to NASA’s Kepler mission, which will begin hunting for them soon.

Interviewer: Did you look at other objects besides disks and planets?

Spitzer: Oh yes, certainly. I have looked at comets in our solar system, the farthest galaxies known, and everything in-between. I was really excited to find hundreds of hidden black holes billions of light-years away. Astronomers had known they were there because they shoot X-rays into space that can be detected as a diffuse glow. But the objects themselves were choked in dust. My infrared eyes, unlike your human eyes, can see through dust, so I was able to round up a lot of these missing black holes.

Interviewer: Is there any other discovery you want to mention?

Spitzer: There are too many to list, but I am particularly proud of this huge mosaic I took of a large swath of our Milky Way galaxy. It looks stunning when you print it out to poster size, and it’s the best view ever of the bustling central portion of our galaxy. You see, the middle of the Milky Way is hopping with stars and dust. It’s chaos, and visible-light cannot escape. These observations not only look cool, they also helped astronomers remap the structure of our galaxy. The new map shows just two spiral arms of stars instead of four as previously believed. How crazy is that!

Interviewer: So what lies ahead?

Spitzer: Well, I’m really looking forward to the warm mission, because now that I have just two infrared channels working, I have more time to look at larger chunks of space for longer periods of time. I can help astronomers answer some really important “big picture” questions, which we didn’t have time for before.

Interviewer: Can you list some specific projects you’ll be working on?

Spitzer: I plan to continue studying exoplanets, including new “hot Jupiters” that Kepler is expected to find. I will also refine estimates of the rate at which our local universe, or space, is expanding. And I will stare at the very distant universe, trying to see some of the farthest objects possible. Oh, and I am also going to survey thousands of asteroids in our neck of the solar system, and get the first real estimate of their size distribution. This will tell us approximately how often big asteroids might come close to Earth.

Interviewer: That sounds scary.

Spitzer: Actually, this information will help us prepare for them. And NASA tracks near-Earth objects diligently. More information can only help.

Interviewer: Will you still take the pretty pictures?

Spitzer: You think my pictures are pretty? Thank you! Yes, I will still snap a lot of pictures. For instance, I will continue to probe cloudy star-forming regions in our galaxy, which often make dramatic pictures.

Interviewer: Anything else you’d like to add?

Spitzer: My cool years have been more than I could ask for, and I look forward to more adventures to come. I’d also like to thank all of the scientists and engineers who have worked so hard to make my mission an ongoing success. And, if any of my fans out there want more info, they can go to www.spitzer.caltech.edu/spitzer.

Posted on by Fraser Cain

Irregular Galaxy

Most galaxies can be categorized by their shape. Our own Milky Way is a spiral galaxy, for example, and the largest galaxies in the Universe are elliptical galaxies. But some galaxies defy categorization. These are the irregular galaxies, and each one is unique in shape, age and structure.

Irregular galaxies are often chaotic in shape, with no central bulge or spiral arms. Although they used to have a more familiar shape, a dramatic collision with another galaxy has distorted their shape.

Astronomers maintain two classifications of irregular galaxies. Irr-I galaxies have some structure, but they’re still distorted enough that they can’t be classified as spiral, elliptical or lenticular shaped. Irr-II galaxies don’t have any structure at all.

The nearby Magellanic Clouds were once thought to be irregular galaxies. Although astronomers have detected a faint barred spiral shape.

There’s only one irregular galaxy in the Messier catalog of objects, and that’s M82; also known as the Cigar Galaxy. It’s located in the constellation Ursa Major about 12 million light-years away, and is famous for its heavy amounts of star formation. In fact, in infrared light, M82 is the brightest galaxy in the sky. Even in visible light, it’s 5 times brighter than the Milky Way.

We have written many articles about galaxies for Universe Today. Here’s an article about Hubble’s recent image of irregular galaxy M82.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

Posted on by Fraser Cain

Elliptical Galaxy

Hubble image of a gas jet blasing from the core of M87. Credit: NASA, ESA, and J. Madrid (McMaster University)

[/caption]
Our own Milky Way is classified as a spiral galaxy. But that’s just one of many classification of galaxies. One of the most common types are elliptical galaxies, named because they have an ellipsoidal (or egg) shape, and a smooth, almost featureless appearance.

Elliptical galaxies are usually large, containing hundreds of millions to trillions of stars. The biggest galaxies in the Universe are elliptical galaxies. They’re the result of many collisions between smaller galaxies, and all these collisions have destroyed the delicate spiral structure that we see in our own galaxy.

And they’re usually old. Elliptical galaxies look redder than spiral galaxies like the Milky Way. That’s because they contain old, red stars and have very low rates of star formation. All of the available gas and dust was already used up in the past, and now all that remains are these old red stars. They also have large populations of globular star clusters.

Elliptical galaxies are usually found in the most violent places in the Universe, like at the heart of galaxy clusters and in compact groups of galaxies. In these places, elliptical galaxies have had an accelerated life, with many galaxy mergers and several periods of star formation. These constant mergers and collisions increased their size and used up all the gas available for star formation.

The smallest dwarf elliptical galaxies are no larger than a globular cluster and can contain a mere 10 million stars. The largest elliptical galaxies can have well over 10 trillion stars. The largest known galaxy in the Universe, M87, is an elliptical galaxy.

We have written many articles about galaxies for Universe Today. Here’s an article about an ancient elliptical galaxy, and another elliptical galaxy where a black hole halted its formation.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.