Hubble Sees an Ancient Elliptical Galaxy

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As galaxies come together through successive mergers they take on the splendid spiral shape like our own Milky Way. Keep merging those larger galaxies, though, and you’ll eventually get an elliptical galaxy – a gigantic diffuse cloud of ancient stars with little structure. Such a galaxy, NGC 1132, was recently photographed by the Hubble Space Telescope.

The elliptical galaxy NGC 1132 belongs in this class of galaxies called “giant ellipticals”. And the galaxy, with its constellation of dwarf galaxies is known as a “fossil group”. They’re the remnants and wreckage from past collisions between large galaxies.

In visible light, NGC 1132 looks like a single, isolated galaxy. But using a technique called gravitational lensing to map out the surrounding dark matter, astronomers found that it resides in a huge cloud of the stuff. In fact, NGC 1132 has as much dark matter as you might find in a group of tens or even hundreds of galaxies.

And once again, in visible light, its stars extend 120,000 light years from its centre. But in the X-ray spectrum, the glow extends 10 times as far – again, similar to a group of galaxies.

So where do fossil groups like this come from? Astronomers think they’re the end product of cosmic collisions, where a single large galaxy consumes all of its neighbors. It’s also possible they’re the result of a strange process, where something stopped moderate galaxies from forming, and only a single large galaxy came together in that region of space.

By analyzing galaxies like this, astronomers will get a better sense of galaxy evolution. It’ll help predict what’s going to happen when the Milky Way and Andromeda collide billions of years in the future.

Original Source: ESA/Hubble News Release

Forget Black Holes, How Do You Find A Wormhole?

Finding a black hole is an easy task… compared with searching for a wormhole. Suspected black holes have a massive gravitational effect on planets, stars and even galaxies, generating radiation, producing jets and accretion disks. Black holes will even bend light through gravitational lensing. Now, try finding a wormhole… Any ideas? Well, a Russian researcher thinks he has found an answer, but a highly sensitive radio telescope plus a truckload of patience (I’d imagine) is needed to find a special wormhole signature…

A wormhole connecting two points within spacetime.
Wormholes are a valid consequence of Einstein’s general relativity view on the universe. A wormhole, in theory, acts as a shortcut or tunnel through space and time. There are several versions on the same theme (i.e. wormholes may link different universes; they may link the two separate locations in the same universe; they may even link black and white holes together), but the physics is similar, wormholes create a link two locations in space-time, bypassing normal three dimensional travel through space. Also, it is theorized, that matter can travel through some wormholes fuelling sci-fi stories like in the film Stargate or Star Trek: Deep Space Nine. If wormholes do exist however, it is highly unlikely that you’ll find a handy key to open the mouth of a wormhole in your back yard, they are likely to be very elusive and you’ll probably need some specialist equipment to travel through them (although this will be virtually impossible).

Alexander Shatskiy, from the Lebedev Physical Institute in Moscow, has an idea how these wormholes may be observed. For a start, they can be distinguished from black holes, as wormhole mouths do not have an event horizon. Secondly, if matter could possibly travel through wormholes, light certainly can, but the light emitted will have a characteristic angular intensity distribution. If we were viewing a wormhole’s mouth, we would be witness to a circle, resembling a bubble, with intense light radiating from the inside “rim”. Looking toward the center, we would notice the light sharply dim. At the center we would notice no light, but we would see right through the mouth of the wormhole and see stars (from our side of the universe) shining straight through.

For the possibility to observe the wormhole mouth, sufficiently advanced radio interferometers would be required to look deep into the extreme environments of galactic cores to distinguish this exotic cosmic ghost from its black hole counterpart.

However, just because wormholes are possible does not mean they do exist. They could simply be the mathematical leftovers of general relativity. And even if they do exist, they are likely to be highly unstable, so any possibility of traveling through time and space will be short lived. Besides, the radiation passing through will be extremely blueshifted, so expect to burn up very quickly. Don’t pack your bags quite yet…

Source: arXiv publication

Using Gravity to Find Planets in the Habitable Zone

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Astronomers have several techniques to discover planets. But one of the least used so far, gravitational microlensing, might be just the right technique to find planets in the habitable zone of nearby dwarf stars.

The first way astronomers find planets is with the radial velocity technique. This is where the gravity of a heavy planet yanks its parent star around so that the wobbling motion too and fro can be measured.

The second technique is through transits. This is where a planet dims the light coming from its parent star as it passes in front. By subtracting the light from when the planet isn’t in front of the star, astronomers can even measure its atmosphere.

The third way is through gravitational microlensing. When two stars are perfectly lined up, the closer star acts as a natural lens, brightening the light from the more distant star. Here on Earth, we see a star brighten in a very characteristic way, and then dim down again. A blip in the change of brightness can be attributed to a planet.

Geometry of a lensing event.
Unlike the other two methods, microlensing allows you to reach out and see planets at tremendous distances – even clear across the galaxy. The problem with microlensing is that it’s a one-time opportunity. You’re never going to see those stars line up in just the same way again.

But Rosanne Di Stefano and Christopher Night from the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA think there’s another way microlensing could be used. In their research paper entitled, Discovery and Study ofNearby Habitable Planets with Mesolensing, the researchers propose that many stars have a high probability of becoming a lens.

Instead of watching the sky, hoping to see a lensing event, you watch specific stars and wait for them to pass in front of a more distant star.

These high-probablility lenses are known as mesolenses. By studying a large number of dwarf stars, they expect that many of them should pass in front of a more distant star as often as once a year. And if pick your targets carefully, like dwarf stars moving in front of the Magellanic Clouds, you might get even more opportunities.

Unlike other methods of planet detection, gravitational lensing relies on light from a more distant star. It is therefore important to ask what fraction of nearby dwarfs will pass in front of bright sources and so can be studied with lensing. Within 50 pc, there are approximately 2 dwarf stars, primarily M dwarfs, per square degree.

For less massive red dwarf stars, you should be able to see them at a distance of 30 light years, and for Sun-mass stars out to a distance of 3,000 light years. These stars are close enough that if a planet is detected in the habitable zone, followup techniques should be possible to confirm the discovery.

They calculated that there are approximately 200 dwarf stars passing in front of the Magellanic Clouds right now. And many of these will have lensing events with the stars in the dwarf galaxies.

Large Magellanic Cloud. Image credit: NASA
Instead of monitoring specific stars, previous surveys have just watched tens of millions of stars per night – hoping for any kind of lensing event. Even though 3,500 microlensing candidates have been discovered so far, they tend to be with stars at extreme ranges. Even if there were planets there, they wouldn’t show up in the observations.

But if you pick your stars carefully, and then watch them for lensing events, the researchers believe you should see that brightening on a regular basis. You could even see the same star brighten several times, and make follow-up observations on its planets.

And there’s another advantage. Both the radial velocity and transit methods rely on the planet and star being perfectly lined up from our vantage point. But a microlensing event still works, even if the planetary system is seen face on.

By using this technique, the researchers think that astronomers should turn up lensing events on a regular basis. Some of these stars will have planets, and some of these planets will be in their star’s habitable zone.

Original Source: Arxiv

Searching for Objects Even Stranger Than Black Holes

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Black holes are already plenty bizarre. Imagine all the mass of several suns compressed down into an object of potentially infinitely small size. But what if you could find an object that’s even stranger: a theoretical “naked singularity”; a black hole spinning so quickly that it lacks an event horizon. A point in space where the density is infinite, yet still visible from the outside.

Here’s the current thinking on black holes. They’re formed when a large star collapses in on itself, lacking the outward pressure to counteract the inward pull of gravity. Once the object reaches a certain size its pull becomes so great that nothing, not even light can escape. The black hole surrounds itself in a shroud of darkness called the event horizon. Any object or radiation that passes through this event horizon is inevitably sucked down into the black hole. And that’s why they’re thought to be black.

But what if that’s not always correct? What if there are circumstances where black holes might not be black at all? It would take some serious spinning, however.

All the black holes discovered so far are thought to be spinning, sometimes more than 1,000 times a second. But in theory, if you could get a black hole spinning ludicrously fast, so that the angular momentum of its spin overcomes the gravitational pull of its mass, it should be able to shed its event horizon. A black hole with 10 times the mass of our Sun would need to be spinning a few thousand times a second.

And here’s the cool part. According to researchers from Duke University and Cambridge, an object spinning like this should be detectable by its gravitational lensing. This is where a massive object, like a black hole, acts like a natural lens to focus the light from a more distant object. If the researchers are right, astronomers should be able to see a telltale signature on the lensed light using existing instruments (or those coming soon).

Their research was published in the September 24th issue of the research journal Physical Review D.

Original Source: Duke University News Release

Most Distant Galaxies Ever Seen

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Astronomers announced today that they’ve located the most distant galaxies ever seen, 13.2 billion light-years away, formed when the Universe was only 500 million years old.

Galaxies that far away can’t easily be seen directly with current telescopes. Instead, the researchers turned massive clusters of galaxies into natural telescopes, using a technique called gravitational lensing. As the light from the more distant galaxies passed the galaxy clusters, it was bent by gravity towards the Earth.

This allowed the (already powerful) 10-metre Keck II telescope to capture additional photons, and measure these distant galaxies. The researchers were able to locate 6 faint star forming galaxies, thanks to the assistance of the gravitational lens, which boosted the signal by about 20 times.

When the Universe was only 300,000 years old, it entered a period called the Dark Ages when no stars were shining. Astronomers have been trying to pinpoint the moment when it came out of this opaque period, and the first stars formed. The combined radiation of these galaxies should be strong enough to break apart the hydrogen atoms around them, ending the Dark Ages. So astronomers could be seeing these galaxies at the moment the Dark Ages ended.

Original Source:Caltech

Spitzer Locates a Binary Pair of Black Holes

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A clever trick has enabled NASA’s Spitzer Space Telescope to calculate the distance to a distant object, confirming that it’s part of our Milky Way. An even more intriguing finding is that the object is probably a binary pair of black holes, orbiting one another – an extremely rare thing to see.

The Spitzer Space Telescope is the only space telescope that orbits the Sun behind the Earth. It’s already 70 million km (40 million miles), and it’s drifting further away every year. This distance between Spitzer and the Earth allows astronomers to look at an object from two different perspectives. Just like our two eyes give us depth perception, two telescopes can measure the distance to an object.

Astronomers noticed that something was causing a star to brighten. The speed and intensity of this brightening matched a gravitational lensing event, where a foreground object’s gravity focuses the light from a more distant star. They imaged the lensing event from here on Earth, but they also called Spitzer into duty to watch as well. Data from the two sources were combined together to determine that the lensing object is inside our galactic halo, and therefore part of its mass.

The light curve of the gravitational lens has led the researchers to believe that they’re looking at two compact objects orbiting one another, quite possibly a binary pair of black holes. It’s also possible that it’s just a pair of regular stars in a neighbouring, satellite galaxy.

Original Source: Spitzer News Release

Podcast: Gravitational Lensing

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Astronomers are always trying to get their hands on bigger and more powerful telescopes. But the most powerful telescopes in the Universe are completely natural, and the size of a galaxy cluster. When you use the gravity of a galaxy as a lens, you can peer right back to the edges of the observable Universe.

Click here to download the episode

Gravitational Lensing – Show notes and transcript

Or subscribe to: astronomycast.com/podcast.xml with your podcatching software.

How Dark Matter Might Have Snuffed Out the First Stars

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What role did dark matter play in the early Universe? Since it makes up the majority of matter, it must have some effect. A team of researchers is proposing that massive quantities of dark matter formed dark stars in the early Universe, preventing the first generations of stars from entering their main sequence stage. Instead of burning with hydrogen fusion, these “dark stars” were heated by the annihilation of dark matter.

And these dark stars might still be out there.

Just a few hundred thousand years after the Big Bang, the Universe cooled enough for first matter to coalesce out of a superheated cloud of ionized gas. Gravity took hold and this early matter came together to form the first stars. But these weren’t stars as we know them today. They contained almost entirely hydrogen and helium, grew to tremendous masses, and then detonated as supernovae. Each successive generation of supernovae seeded the Universe with heavier elements, created through the nuclear fusion of these early stars.

Dark matter dominated the early Universe too, hovering around normal matter in great halos, concentrating it together with its gravity. As the first stars gathered together inside these halos of dark matter, a process known as molecular hydrogen cooling helped them collapse down into stars.

Or, that’s what astronomers commonly believe.

But a team of researchers from the US think that dark matter wasn’t just interacting through its gravity, it was right there in the thick of things. Their research is published in the paper “Dark matter and the first stars: a new phase of stellar evolution“. Particles of dark matter compressed together began to annihilate, generating massive amounts of heat, and overwhelming this molecular hydrogen cooling mechanism. Hydrogen fusion was halted, and a new stellar phase – a “dark star” – began. Massive balls of hydrogen and helium powered by dark matter annihilation, instead of nuclear fusion.

If these dark stars are stable enough, it’s possible that they could still exist today. That would mean that an early population of stars never reached the Main Sequence stage, and still live in this aborted process, sustained by the annihilation of dark matter. As the dark matter is consumed in the reaction, additional dark matter from surrounding regions could flow in to keep the core heated, and hydrogen fusion might never get a chance to take over.

Dark stars might not be so long lasting, however. The fusion from regular matter might eventually overwhelm the dark matter annihilation reaction. Its evolution into a regular star wouldn’t be halted, only delayed.

How could astronomers search for these dark stars?

They would be very large, with a core radius larger than 1 AU (the distance from the Earth to the Sun), so they might be candidates for gravitational lensing experiments. These observations use the gravity from nearby galaxies to serve as an artificial telescope to focus the light from a more distant object. This is the best technique astronomers have to find the most distant objects.

They could also be detectable by the annihilation products of the dark matter. If the nature of dark matter matches the Weakly Interacting Massive Particles theory, its annihilation would give off very specific radiation and particles in large quantities. Astronomers could look for gamma-rays, neutrinos, and antimatter.

A third way to detect them would be to search for a delay in the transition to the Main Sequence stage for the early stars. The dark stars could have interrupted this stage for millions of years, leading to an unusual gap in stellar evolution.

Perhaps these dark stars will give astronomers the evidence they need to finally know what dark matter really is.

Original Source: Dark matter and the first stars: a new phase of stellar evolution

Use Galactic Gravitational Lenses to Really See the Universe

Galactic lens in action. Image credit: CFHTTo see any distance in space, you need some kind of telescope. We’ve got some pretty powerful ones here on Earth, but nature has us beat with gravitational lenses. This is a phenomenon when a relatively nearby object passes directly between us and a more distant object. The gravity from the nearby object acts as like a telescope lens to bend light and magnify the more distant object.
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Astronomers Peer Inside a Quasar

Quasars are some of the brightest objects in the Universe, and astronomers believe they’re caused by the outpouring of radiation from the environment around an actively feeding supermassive black hole. New research using the Chandra X-Ray Observatory has looked inside a quasar, to see the disk of material spiraling into the black hole. Astronomers used the gravity from a relatively nearby galaxy as a gravitational lens to focus the light from the more distant quasar, giving this impressive view.
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