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.

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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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Galaxy Collision Separates Out the Dark Matter

There’s more dark matter than regular matter in the Universe, and they’re normally all mixed up together in galaxies. But astronomers using the Chandra X-Ray Observatory have found a situation where dark matter and normal matter can be wrenched apart. In a collision between giant galaxy clusters, hot gas clouds in the clusters encounter friction as they pass through one another, separating them from the stars. The dark matter isn’t affected by this friction either, so astronomers were able to calculate the effect of its gravity on regular matter.
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Hubble Finds an Exoplanet’s Parent Star

When a star flared briefly, astronomers knew it was because a dimmer star had passed directly in front, acting as a lens with its gravity to focus light. Unfortunately, they couldn’t find the star. This was important, because the brief microlensing event also turned up the fact that this lensing star has a planet. Astronomers have used the power of the Hubble Space Telescope to find this dim star two years after the lensing event. Identifying the star is critical, because it allows astronomers to measure its unique characteristics, such as mass, temperature and composition.
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Podcast: A Puzzling Difference

Imagine looking at red houses, and sometimes you see a crow fly past. But every time you look at a blue house, there’s always a crow flying right in front of the house. The crow and the house could be miles apart, so this must be impossible, right? Well, according to a new survey if you look at a quasar, you’ll see a galaxy in front 25% of the time. But for gamma ray bursts, there’s almost always an intervening galaxy. Even though they could be separated by billions of light years. Figure that out. Dr. Jason X. Prochaska, from the University of California, Santa Cruz speaks to me about the strange results they’ve found, and what could be the cause.
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