Universe Today

May 4, 2009January 30, 2017 by Fraser Cain

What is the Local Group?

Local Group of galaxies, including the massive members M31 (Andromeda Galaxy) and Milky Way, as well as other nearby galaxies. Credit: Wikipedia Commons/Antonio Ciccolella

The Milky Way is just one galaxy located in a vast cluster of galaxies known as the Local Group. This group contains more than 50 galaxies (mostly dwarf galaxies). The total size of the Local Group is 10 million light-years across, and it’s estimated to have a mass of 1.29 billion solar masses. The Local Group is just one collection of galaxies in the even bigger Virgo Supercluster.

The largest, most massive galaxies in the Local Group are the Milky Way, Andromeda and the Triangulum Galaxy.

Each of these galaxies has a collection of satellite galaxies surrounding them. For example, the Milky Way has Sagittarius Dwarf Galaxy, Large Magellanic Cloud, Small Magellanic Cloud, Canis Major Dwarf, Ursa Minor Dwarf, Draco Dwarf, Carina Dwarf, Sextans Dwarf, Sculptor Dwarf, Fornax Dwarf, Leo I, Leo II, and Ursa Major Dwarf.

Andromeda has satellite galaxies M32, M110, NGC 147, NGC 185, And I, And II, And III, And IV, And V, Pegasus dSph, Cassiopeia Dwarf, And VIII, And IX, and And X.

The Traingulum galaxy might be a satellite to Andromeda, and it might also have the Pisces Dwarf as a satellite.

The other members of the Local Group, not associated with another galaxy, include: IC10, IC1613, Phoenix Dwarf, Leo A, Tucana Dwarf, Cetus Dwarf, Pegasus Dwarf Irregular, Wolf-Lundmark-Melotte, Aquarius Dwarf, and Sagittarius Dwarf Irregular.

The first astronomer to identify the Local Group was Edwin Hubble, who called the collection the Local Group in his book, The Realm of Nebulae. Of course, at this time Hubble didn’t know that they were distant galaxies, separate from our own Milky Way, so he called them nebulae.

We have written many articles about galaxies for Universe Today. Here’s an article about a dwarf galaxy falling into the local group, and here’s an article about how the Universe doesn’t seem to be expanding evenly.

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.

May 4, 2009December 24, 2015 by Nancy Atkinson

Is a Nearby Object in Space Beaming Cosmic Rays at Earth?

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Data from several different space and ground based observatories imply the presence of a nearby object that is beaming cosmic rays our way. Scientists with the Fermi Space Telescope say an unknown pulsar may be close by, sending electrons and positrons towards Earth. Or another more exotic explanation is that the particles could come from the annihilation of dark matter. But whatever it is, the source is relatively close, surely in our galaxy. “If these particles were emitted far away, they’d have lost a lot of their energy by the time they reached us,” said Luca Baldini, a Fermi collaborator.

Comparing data from the Fermi space telescope with results from the PAMELA spacecraft and the High Energy Stereoscopic System (H.E.S.S.) ground-based telescope, the three observatories have found surprisingly more particles with energies greater than 100 billion electron volts (100 GeV) than expected based on previous experiments and traditional models.

Fermi is primarily a gamma ray detector, but its Large Area Telescope (LAT) is also tool for investigating the high-energy electrons in cosmic rays.

Video of the LAT detecting high energy particles.

Cosmic rays are hyperfast electrons, positrons, and atomic nuclei moving at nearly the speed of light. Unlike gamma rays, which travel from their sources in straight lines, cosmic rays wend their way around the galaxy. They can ricochet off of galactic gas atoms or become whipped up and redirected by magnetic fields. These events randomize the particle paths and make it difficult to tell where they originated. But determining cosmic-ray sources is one of Fermi’s key goals.

Using the LAT, which is sensitive to electrons and their antimatter counterparts, positrons, the telescope looked at the energies of 4.5 million cosmic rays that struck the detector between Aug. 4, 2008, and Jan. 31, 2009 and found more of the high-energy variety than expected, those with more than 1 billion electron volts (eV).

A spokesman from the Goddard Space Flight Center said the exact number of how many more is not currently available, due to peculiarities of the data.

But results from Fermi also refute other recent findings from a balloon-borne experiment. The Advanced Thin Ionization Calorimeter (ATIC) captured evidence for a dramatic spike in the number of cosmic rays at energies around 500 GeV from its high atmospheric location over Antarctica. But Fermi did not detect these energies.

“Fermi would have seen this sharp feature if it was really there, but it didn’t.” said Luca Latronico, a team member at the National Institute of Nuclear Physics (INFN) in Pisa, Italy. “With the LAT’s superior resolution and more than 100 times the number of electrons collected by balloon-borne experiments, we are seeing these cosmic rays with unprecedented accuracy.”

“Fermi’s next step is to look for changes in the cosmic-ray electron flux in different parts of the sky,” Latronico said. “If there is a nearby source, that search will help us unravel where to begin looking for it.”

Source: NASA

May 4, 2009September 15, 2016 by Fraser Cain

What is Intergalactic Space?

The space between stars is known as interstellar space, and so the space between galaxies is called intergalactic space. These are the vast empty spaces that sit between galaxies. For example, if you wanted to travel from the Milky Way to the Andromeda galaxy, you would need to cross 2.5 million light-years of intergalactic space.

Intergalactic space is as close as you can get to an absolute vacuum. There’s very little dust and debris, and scientists have calculated that there’s probably only one hydrogen atom per cubic meter. The density of material is higher near galaxies, and lower in the midpoint between galaxies.

Galaxies are connected by a rarefied plasma that is thought to posses a cosmic filamentary structure, which is slightly denser than the average density of the Universe. This material is known as the intergalactic medium, and it’s mostly made up of ionized hydrogen. Astronomers think that the intergalactic medium is about 10 to 100 times denser than the average density of the Universe.

This intergalactic medium can actually be seen by our telescopes here on Earth because it’s heated up to tens of thousands, or even millions of degrees. This is hot enough for electrons to escape from hydrogen nuclei during collisions. We can detect the energy released from these collisions in the X-ray spectrum. NASA’s Chandra X-Ray Observatory – a space telescope designed to search for X-rays – has detected vast clouds of hot intergalactic medium in regions where galaxies are colliding together in clusters.

We have written many articles about galaxies for Universe Today. Here’s an article about how intergalactic dust might be messing up observations, and here’s an article about a cosmic hurricane in a starburst galaxy.

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.

May 4, 2009December 24, 2015 by Fraser Cain

Quasars

When astronomers first started using radio telescopes in the 1950s to study the Universe, they discovered a strange phenomenon. They found objects that shone brightly in the radio spectrum, but they couldn’t see any visible object associated with them. They called them quasi-stellar radio sources, or “quasars” for short.

Within a decade of their discovery, astronomers learned that these quasars were moving away at tremendous velocities. This velocity, or red-shift of their light, indicated that they were billions of light-years away; beyond the capabilities of most optical telescopes. It wasn’t until the 1960s when a quasar was finally tied to an optical object, a distant galaxy.

Since then, thousands of quasars have been discovered, but astronomers had no idea what they were. Finally in the 1980s, astronomers developed unified models that identified quasars as active galaxies. The bright radiation coming from them is because of the accretion disks surrounding the supermassive black holes at their centers. We see a quasar when a supermassive black hole is actively feeding on the surrounding material.

Since our own Milky Way has a supermassive black hole, it’s likely that we have gone through many active stages, whenever material is falling into the black hole; our galaxy would be seen as a quasar. But other times, like now, the supermassive black hole is quiet.

With new powerful telescopes, astronomers have observed that some quasars have long jets of material firing out from the center of the galaxy. These are channeled by the magnetic fields created by the supermassive black hole’s rotation in the accretion disk. The most luminous quasars can exceed the radiation output of an average quasar.

We have written many articles about quasars for Universe Today. Here’s an article about the first triple quasar ever found, and some hidden quasars… found!

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.

May 3, 2009December 24, 2015 by Ian O'Neill

2009 HC82: A Burnt-Out, Eccentric and Backward Near-Earth Asteroid

The Solar System often throws up surprises for astronomers, but the recent discovery of a 2- to 3-km wide asteroid called 2009 HC82 has sent observers in a spin. A retrograde spin to be precise.

This particular near-Earth asteroid (NEO) should have already been spotted as it has such a strange orbit. It is highly inclined, making it orbit the Sun backwards (when compared with the rest of the Solar System’s planetary bodies) every 3.39 years. What’s more, it ventures uncomfortably close (3.5 million km) to the Earth, making this NEO a potentially deadly lump of rock…

2009 HC82 was discovered on April 29th by the highly successful Catalina Sky Survey, and after independent observations by five different groups, it was determined that the asteroid has an orbit of 3.39 years and that its orbit is very inclined. So inclined in fact that the asteroid’s orbit takes it well out of the Solar System ecliptic at an angle of 155°. Inclined orbits aren’t rare in themselves, but if you find an asteroid with an inclination of more than 90°, you are seeing a very rare type of object: a retrograde asteroid.

The last time I wrote about a retrograde asteroid was back in September 2008 (Kuiper Belt Object Travelling the Wrong-Way in a One-Way Solar System), when a University of British Columbia researcher spotted a rather unique retrograde Kuiper belt object (called 2008 KV42) that had a large looping orbit with an inclination larger than 90°. It was nicknamed “Drac” after Dracula’s ability to walk on walls.

2009 HC82 is therefore not only rare, it is also very strange. It orbits the Sun the wrong way (therefore making it very inclined), it is a potentially hazardous NEO (it is smaller than the 10 km asteroid that is attributed to wiping out the dinosaurs, but it would cause significant devastation on a global scale if it did hit us) and it is very eccentric.

All these orbital components have led to speculation that 2009 HC82 is in fact a “burnt out” comet. Comets originate from the Oort Cloud, a theoretical region cometary nuclei that occasionally gets nudged by gravitational disturbances when stars pass by. The Oort Cloud is not restricted to a belt along the ecliptic (like the asteroid belt or the Kuiper belt), it encapsulates our Solar System. Therefore, this may explain 2009 HC82’s bizarre trajectory; it was a comet, but all the ice has vaporized, leaving a rocky core to fling around the Sun on a death-defying orbit, buzzing the inner Solar System.

Brian Marsden of the Minor Planet Center agrees that some retrograde asteroids could be burnt-out comets. The size and shape of the new asteroid’s orbit “is very like Encke’s comet except for inclination,” he said, but the only difference is the fact that 2009 HC82 has no cometary tail.

More observations are needed before a definitive conclusion can be made, but Marsden is confused as to why this object has not been discovered before now. “It should have been easily observable in 2000,” says Marsden. “Why wasn’t it seen then?”

It is hoped further investigation may answer this question…

Source: New Scientist

May 2, 2009December 24, 2015 by Fraser Cain

Galaxy Pictures

Spiral galaxy M101. Image credit: Hubble

The best photographs captured from ground and the Hubble Space Telescopes. I could look at pictures of beautiful spiral galaxies all day. So let’s take a look at some of the most beautiful galaxy photos ever taken.

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This is a classic picture of the spiral galaxy M101, captured by the Hubble Space Telescope. Since this galaxy is seen almost face-on, it allows astronomers to see what a large spiral galaxy, like our own Milky Way, looks like. M101 is located in the constellation of Ursa Major and measures 170,000 light-years across; twice the diameter of the Milky Way.

This is the Andromeda Galaxy, also known as M31. It’s the closest large galaxy to the Milky Way; in fact, Andromeda is currently on a collision course with the Milky Way, and will collide with us in about 10 billion years. After that, the two galaxies will collect together into an enormous irregular galaxy, and our supermassive black holes will merge together.

Andromeda galaxy photo. Image credit: Spitzer

Here’s another Andromeda galaxy picture, but this time captured in the infrared spectrum by the Spitzer Space Telescope. By seeing Andromeda in infrared, astronomers can see regions that would normally be obscured by dust, like new star forming regions, or the center of the galaxy.

This is a photo of galaxy M81 captured by the Hubble Space Telescope. This is another example of a grand spiral galaxy, seen from a bit of an angle. This galaxy is located 11.6 million light-years away in the constellation Ursa Major.

Here’s a picture of the galaxy Centaurus A, located in the constellation of the same name. The huge sprays of material above and below the galaxy demonstrate the power of the supermassive black hole located at the heart of the galaxy. The jets of material extend more than 13,000 light-years away from the center of the galaxy.

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.

May 1, 2009December 24, 2015 by Nancy Atkinson

NASA Begins Job Layoffs As Shuttle Retirement Looms

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NASA began the first round of job layoffs today as the space agency prepares to retire its fleet of space shuttles. 160 people were notified today their jobs were being cut, the first of 900 jobs that will evaporate in the next five months. The first wave of layoffs will affect Lockheed Martin and ATK Thiokol, contractors that support the shuttle program building fuel tanks and rocket boosters in Louisiana and Utah. The shuttle program employs about 1,600 NASA civil servants across the space agency and 13,800 contractors around the country. Once the shuttle stops flying, as many as 6,500 jobs could be cut at the Kennedy Space Center alone.

NASA announced the first round of layoffs at a briefing Thursday, where they also announced the launch date for the Hubble Telescope repair mission as May 11, a day earlier than previously planned. Making the two divergent announcements at the same news conference was bittersweet.

Officials at the briefing stressed that without an infusion of money in 2010 — for which a detailed budget is expected to be released next week — they had no choice but to continue the gradual shutdown of shuttle operations.

Bill Gerstenmaier (left), NASAÂ?s associate administrator for space operations, and shuttle-program manager John Shannon announce job cuts Thursday at Kennedy Space Center. Credit: NASA

Shuttle program manager John Shannon said several hundred jobs will be lost to attrition and some employees will transfer to other contractors or projects. The rest will be layoffs.

“Only if we were directed to fly additional missions would we halt that activity,” Shannon said.

Bill Gerstenmaier, associate administrator for space operations, said that if $2.5 billion proposed recently by Congress budget planners materialized, it could allow a few shuttles to fly past the 2010 retirement date if some shuttle flights got delayed and NASA were unable to complete the construction of the international space station.

He added that, although the shuttle program’s plans were clear, it was less certain how quickly jobs would ramp up for the shuttle’s replacement, the Ares I rocket and Orion capsule.

The first launch of Ares I and Orion is planned for March 2015, but that date is not certain.

Source: Orlando Sentinel

May 1, 2009December 24, 2015 by Nancy Atkinson

Why Are Galaxies Smooth? Star Streams

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Look at the disk of any large spiral galaxy, and outwardly it appears smooth, with stars evenly distributed throughout. But when young stars are forming, they are clustered together in dense clouds of dust and gas. So what happens as the galaxy matures to allow for the smooth distribution seen in galaxies like the Milky Way? Using NASA’s Spitzer Space Telescope, an international team of astronomers has discovered streams of young stars flowing from their natal cocoons in distant galaxies. These distant rivers of stars provide an answer to one of astronomy’s most fundamental puzzles.

Astronomers know that the clusters where stars form begin to disappear when their ages reach several hundred million years. A few mechanisms are thought to explain this: some clusters evaporate when random internal motions kick out stars one by one, and other clusters disperse as a result of collisions among the clouds where they were born. Zooming out to mechanisms operating on larger scales still, shearing motions caused by the galaxy’s rotation around its center disperses the clusters of clusters of young stars.

“Our analysis now answers the grand puzzle. By finding a myriad of streams of young stars all over the disks of galaxies we studied, we see that the mechanism for pulling the clusters of young stars apart is shearing motions of the parent galaxy. These streams are the ‘missing link’ we needed to understand how the disks of galaxies evolve to look the way they do,” said team leader David Block of the University of the Witwatersrand in South Africa.

Crucial to this discovery was finding a way to image previously hidden young stellar streams in galaxies millions of light-years away. To do this the team used high-resolution infrared observations from the Spitzer.
Using infrared rather than visible light to look at the galaxies allowed the group to pick out stars at just the right age when the stars are just starting to spread out from their clusters.

“Spitzer observes in the infrared where 100-million-year-old populations of stars dominate the light,” noted co-author Bruce Elmegreen, from IBM’s Research Division in New York. “Younger regions shine more in the visible and ultraviolet parts of the spectrum, and older regions get too faint to see. So we can filter out all the stars we don’t want by taking pictures with an infrared camera.”

Infrared is also important because light in this part of the spectrum can penetrate the dense dust clouds surrounding the clusters where stars form.

“Dust blocks optical starlight very effectively,” said Robert Gehrz of the University of Minnesota, “but infrared light with its longer wavelength goes right around the dust particles blocking our view. This allows the infrared light from young stars to be seen more clearly.”

But even when the images are taken in the infrared, they are still dominated by the light from the smooth older disks of galaxies, not the faint tracks of young dispersing clusters. Special mathematical manipulations were needed to pick out the clusters, whose faint tracks can still be seen precisely because they are not smooth.

Team member Ivanio Puerari of the Instituto Nacional de Astrofisica, Optica y Electronica in Puebla, Mexico used a technique invented by mathematician Jean Baptiste Fourier in the early 1800’s. The technique is effectively a spatial filter that picks out structure on the physical scale where star formation occurs. “The structures cannot be seen on the original Spitzer images with the human eye,” noted Puerari.

“The combination of the Fourier filtering and infrared images highlighted regions of just the right size and the right age. To then unveil so many star streams in the disks of galaxies was unimaginable a year ago. This discovery continues to highlight the enormous potential of the Spitzer Space Telescope to make contributions none of us could have dreamed possible,” commented Giovanni Fazio from the Harvard-Smithsonian Center for Astrophysics, project leader for the Spitzer Infrared Array Camera team used to take the pictures, and co-author of the discovery.

“Galileo, as both astronomer and mathematician, would have been proud. It is a wonderful interplay between the use of astronomical observations and mathematics and computers, exactly 400 years since Galileo used his telescope to examine our Milky Way galaxy in 1609,” Fazio said

Source: Spitzer

May 1, 2009December 24, 2015 by Nancy Atkinson

Coastal Formations Not Result of Asteroid Impact

The black arrows indicate the orientation of chevrons along the southern coast of Madagascar, but the white arrows indicate what computer models say should have been the orientation if they were caused by the impact of a space body in the Indian Ocean. Credit: Robert Weiss

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Coastal formations called chevrons, large U- or V-shaped features found on coastlines around the world were originally thought to be evidence of ancient “megatsunamis” caused by asteroids or comets slamming into the ocean. However, new research using Google Earth and computer models to recreate large wave action refutes that school of thought.

The theory of chevrons being created by tsunamis was proposed in 2006 after the structures were found in Egypt and the Bahamas. Some were, at places, between several hundred meters- and a kilometer-wide. Since they were also found to exist in Australia and Madagascar, some geologists formed the hypothesis that they were sediment cones left behind by large tsunamis, perhaps up to ten times stronger than the devastating tsunami in the Indian Ocean in December 2005.

The theory propsed the only source for such a megatsunami was a meteor impact, occurring about 5,000 years ago.

But a new study, led by Jody Bourgeois, a geologist and tsunami expert at the University of Washington, argues that this theory is simply “nonsense. For example, she said, there are numerous chevrons on Madagascar, but many are parallel to the coastline. Models created by Bourgeois’ colleague Robert Weiss show that if they were created by tsunamis they should point in the direction the waves were travelling, mostly perpendicular to the shore.

Landsat image of the Fenambosy Chevrons in Madagascar by USGS. The open side of these chevrons point directly at a crater at the bottom of the Indian Ocean. They suggest a gigantic meteor impact occurred about 4800 years ago. But new research says chevrons were likely formed by wind.

“And if it really was from an impact, you should find evidence on the coast of Africa too, since it is so near,” she said.

By using Google Earth, Bourgeois and her team searched for chevrons and surprisingly they found some in desert areas, well inland and away from the shores.

“The extraordinary claim of ‘chevron’ genesis by megatsunamis cannot withstand simple but rigorous testing. There are the same forms in the Palouse in eastern Washington state, and those are clearly not from a tsunami,” Bourgeois said.

She believes the structures were formed by wind.

The discovery of marine fossils in some chevron formations seems to support the idea that a wave created the deposit, but Bourgeois discounts that evidence also.

“Marine fossils can get into non-marine deposits. It’s not uncommon. You only have to change sea level a little bit or have them wash up on a beach in a storm,” she said. “And some marine organisms can be carried by the wind. I am convinced these are largely wind-blown deposits.”

She noted that similar deposits have been seen on the Kamchatka Peninsula on Russia’s east coast, where she has conducted research for more than a decade.

“Those are made of volcanic ash, and they are not near the coast at all, yet they look very similar to these coastal chevrons,” Bourgeois said.

Source: Newswise

May 1, 2009December 24, 2015 by Fraser Cain

Spiral Galaxy

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When you think of a galaxy, you’re probably thinking of a spiral galaxy. You know, with the central bulge and grand sweeping arms that spiral outward from the center. In fact, our own Milky Way is a spiral galaxy, and there are many others out there in the Universe. But have you ever thought about how they form in such a beautiful shape?

A spiral galaxy is shaped like a flat disk with a thicker bulge in the center. Bright spiral arms start from the center and then coil outward like a pinwheel. All spiral galaxies rotate, but very slowly; our own Milky Way completes a single revolution once every 250 million years or so.

The spiral arms are actually density waves that move around the disk of the spiral galaxy. As the density wave passes over a region, masses are pulled together, and you get bright pockets of star formation. Then the density wave moves on, and encourages another region to begin star formation.

The central bulge at the center of a spiral galaxy contains older stars, similar to an elliptical galaxy. And at the very center, there’s always a supermassive black hole containing millions of times the mass of the Sun.

Spiral galaxies are also surrounded by a vast spheroidal halo of stars. These stars might not have formed in the galaxy, but were stolen through successive mergers with other galaxies. This galactic halo also contains many globular star clusters.

Astronomers think that spiral galaxies are slowly built over time through the merger of smaller galaxies. As these tiny galaxies came together, their total momentum set the merged galaxy spinning. This spin flattened out the galaxy and set the spiral arms in motion.

We have written many articles about the galaxies for Universe Today. Here’s an article with twin spiral galaxies interacting, and here’s spiral galaxy NGC 2403.

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.