Astronomy Archives

May 15, 2007March 3, 2023 by Fraser Cain

Ring of Dark Matter Discovered Around a Galaxy Cluster

Astronomers using the Hubble Space Telescope have turned up a ghostly ring of dark matter, surrounding the aftermath of a collision between two galaxy clusters. This is one of the strongest pieces of evidence ever found for the existence of dark matter; a shadowy substance that only interacts with regular matter through gravity.

Researchers discovered the ring while they were mapping the distribution of dark matter inside the galaxy cluster Cl 0024+17, which is located about 5 billion light-years from Earth. The ring itself is 2.6 million light-years across.

Since dark matter is invisible, the researchers discovered the ring by its gravitational influence on background galaxies. The more dark matter concentrated into an area, the more the light from background objects is distorted, like ripples on a pond of water. We’re fortunate that the head-on collision between the galaxy clusters provided us with a perfect view from our perspective here on Earth.

So how did this ring form? Simulations have shown that when galaxy clusters collide, the dark matter falls into the centre of the combined cluster, and then sloshes back out. As it heads back out, mutual gravity slows it back down, and the dark matter piles up into a ring.

Original Source: Hubble News Release

May 11, 2007December 26, 2015 by Fraser Cain

Dwarf Galaxies Have a Large Amount of Unseen Matter

Astronomers have found that the cosmic wreckage left over when large galaxies collide have an unusually high amount of unseen matter in them. In some situations, these dwarf galaxies have twice the matter that astronomers would expect.

The research was done using the National Science Foundation’s Very Large Array (VLA) radio telescope to study a galaxy called NGC 5291, located about 200 million light-years from Earth. About 360 million years ago, this galaxy collided with another, and the collision sent out streams of stars, gas and dust. These streams later coalesced into dwarf galaxies that orbit the parent galaxy.

Under the VLA survey, astronomers studied three of these dwarf galaxies, and found that they have two to three times the amount of dark matter as visible matter. Astronomers don’t actually think this is the mysterious non-interacting dark matter that makes up the bulk of matter in the Universe. Instead, it’s cold hydrogen molecules which are extremely difficult to see.

This cold molecular hydrogen likely came from the disks of the galaxies, and not the haloes.

Original Source: NRAO News Release

May 11, 2007December 26, 2015 by Fraser Cain

A Star as Old as the Universe

The Universe is thought to be 13.7 billion years old. So it was quite a surprise when astronomers turned up a star that’s 13.2 billion years old. That means it formed only a few hundred million years after the Big Bang.

The star, HE 1523-0901, was discovered by the European Southern Observatory’s VLT. Astronomers knew right away that that had an old star, but the technique for dating it accurately is pretty difficult. The method is similar to radiocarbon dating, where archaeologists use the approximate quantities of carbon isotopes to measure the age of ancient artifacts.

In this situation, though, the astronomers used the VLT to measure the abundance of the various radioactive elements, like thorium and uranium. Once the star originally formed, its radioactive elements began to decay, changing into other elements. By knowing the rate of decay, and being able to measure these elements so accurately, they were able to peg the ages of the star at 13.2 billion years old. The trick was to find elements that decay at a set rate, but would still be around after billions of years of decay.

Original Source: ESO News Release

May 10, 2007December 26, 2015 by Fraser Cain

When Our Galaxy Smashes Into Andromeda, What Happens to the Sun?

When astronomers look into the night sky, almost every single galaxy is speeding away from us, carried by the expansion of the Universe. There’s one notable exception; though, the massive Andromeda galaxy (aka M31), which is speeding towards us at a rate of 120 km/s. And some time in the next few billion years, our two galaxies will collide and begin the lengthly process of merging together. Our Sun, and even the Earth should still be around, so it begs the question, what will happen to our Solar System?

Fortunately, T. J. Cox and Abraham Loeb from the Harvard-Smithsonian Center for Astrophysics have done the math in their recent paper entitled The Collision Between The Milky Way And Andromeda. In this paper, they chart out their simulation of this massive collision, and estimate some future fates for our Solar System.

Our galaxy, the Milky Way, and Andromeda (M31) together with their 40 smaller companions make up the two largest members of the Local Group of galaxies. While most galaxies are hurtling away from us as part of the expansion of the Universe, the Local Group is gravitationally bound together, and will continue to interact over the coming years.

When our Sun was born, 4.7 billion years ago, Andromeda and the Milky Way were 4.2 million light-years apart. Steadily moving together over the billions of years, they’re now only 2.6 million light-years apart and clearly headed for a collision. But it won’t be a head-on collision, the two galaxies will take swipes at each other first.

The first sideswipe will occur less than 2 billion years from now. During that first interaction, there’s a 12% chance that the Solar System might get ejected from the disk of the Milky Way, and spun out into the tidal tail of material that will stream out from the Milky Way. And there’s a remote chance, less than 3%, that the Sun will jump ship, joining up with Andromeda, and leaving the Milky Way entirely.

Since the Sun and the Earth will still be around, future astronomers could witness the collision in all its glory. Since the Sun will be steadily increasing its output of radiation, life might not be able to survive on our planet if engineers can’t figure out a way to keep the Earth moving away from the Sun.

Then the galaxies will come back together for another swipe, and then another, and eventually settle down into a gigantic swarm of stars buzzing around a common center of gravity. Currently quiet, the twin supermassive black holes may flare up, becoming active galactic nuclei, feasting on the torrent of new material that was unlucky to enter their feeding zones. Colliding clouds of gas and dust will flare up in furious regions of star formation.

In all likelihood, these interactions will push the Sun out into the new galaxy’s outer halo, pushing us at least 100,000 light years from the centre, and safely way from those twin black holes.

And 7 billion years from now, when our Sun is in the last stages of life – a red giant – and our Earth is a burned cinder, Milkomeda will have formed.

(At least, that’s what Cox and Loeb are calling it. I coined Milkdromeda in an episode of Astronomy Cast.)

This future galaxy will be a massive, elliptical galaxy, losing any remnant of its familiar spiral arms. The furious star formation will settle down, and this new galaxy will live out its remaining years, slowly using up its remaining raw stellar material.

100 billion years from now, all galaxies not bound to the Local Group will recede from vision – now traveling away from us faster than the speed of light. The concept of extragalactic astronomy will end, and Milkomeda will account for the entire visible Universe.

Original Source: Arxiv

May 8, 2007December 26, 2015 by Fraser Cain

How Dark Matter Might Have Snuffed Out the First Stars

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

May 7, 2007December 26, 2015 by Fraser Cain

Chandra Sees the Brightest Supernova

NASA’s Chandra X-Ray observatory might have observed a brand new kind of supernova, or maybe it’s just an unusually bright supernova. Whatever the case, the explosion of SN 2006gy seems to be the brightest supernova ever observed, flaring with 100 times the energy of a typical exploded star.

The team that discovered SN 2006gy think that the original star might have contained 150 times the mass of our Sun; only the first generation of stars that formed after the Big Bang were thought to be this massive. It was the Chandra X-Ray observations that helped distinguish the supernova as originating from a massive star, and not the Type 1A associated with an exploding white dwarf star.

A supernova occurs when a massive star consumes its fuel, loses outward pressure, and collapses inward under its own gravity. But in the case of SN 2006gy, there might be an entirely new process going on here. The precursor star could have been so large that its core produces a large amount of gamma rays. The energy from this radiation is converted into particle and anti-particle pairs, and causes a drop in energy. Without this energy, the star collapses from its own gravity early and detonates as a supernova.

Even though SN 2006gy is the intrinsically brightest supernova ever seen, it exploded in galaxy NGC 1260, which is located about 240 million light-years away – so you need a powerful telescope to see it. The closest star that’s in the same category is Eta Carinae, a massive star located only 7500 light-years away. No telescope will be necessary when it explodes.

Original Source: Chandra News Release

May 3, 2007March 3, 2023 by Fraser Cain

Multiple Generations of Stars in a Cluster

Astronomers have long believed that globular star clusters formed out of a single cloud of dust and gas. All the stars in the cluster should be roughly the same age. But new observations from the Hubble Space Telescope show this isn’t always the case – in cluster NGC 2808, there were three distinct periods of star formation.

Globular star clusters are some of the most ancient objects in the Universe, forming shortly after their parent galaxies came together. They’re compact swarms with hundreds of thousands of stars held together by mutual gravity. The traditional view is that these clusters formed together, from the same material, at the same time, and then evolved together over time.

These new Hubble observations show that there are clearly three different populations of stars in globular cluster NGC 2808. All of the stars formed within 200 million years of each other. Each generation contains a different mix of chemicals, with increasing quantities of helium.

One theory is that the clusters hung onto large quantities of gas, beyond that initial period of star formation. Some event, or shockwaves from supernovae might have collapsed this gas, mixing in heavier elements to create additional stars. Another possibility is that NGC 2808 isn’t a globular cluster at all, but an ancient dwarf galaxy that was stripped of most of its material when it was captured by the Milky Way.

Original Source: Hubble News Release

May 3, 2007March 3, 2023 by Fraser Cain

Super-Massive Planet Discovered

It’s been a week of planetary discoveries. Here’s another. This latest find announced by the Harvard-Smithsonian Center for Astrophysics (CfA) is the most massive planet ever discovered. This gas giant, named HAT-P-2b, weighs in at 8 times the mass of Jupiter.

HAT-P-2b was discovered using the transit method. In other words, it was discovered because it dims the light from its parent star as it passes in front. Astronomers have calculated that it has a very unusual elliptical orbit, getting as close as 5 million km (3.1 million miles) and then swinging out to 15 million km (9.6 million miles). But this journey only takes 5.63 days.

As planets go, this is a strange one. It has 8.2 times the mass of Jupiter, but it’s only 1.18 times the size of Jupiter. It has roughly the density of the Earth, but it’s made up almost entirely of hydrogen. In fact, it’s right at the boundary between planet and star. With only another 50% more mass, it would have begun nuclear fusion.

The discovery was made using a network of small, automated telescopes called HATNet. There are a total of six telescopes; four at the Whipple Observatory in Arizona, and two more in Hawaii. These robotic telescopes make 26,000 observations every night, searching for stars that dip in brightness on a regular basis.

Original Source: CfA News Release

May 3, 2007March 3, 2023 by Fraser Cain

Young Stars Trashing Their Nursery

The latest image released from the Spitzer Space Telescope shows a pair of stars destroying their surroundings with powerful jets of radiation. The stars are located about 600 light-years away in a nebula called BHR 71. The image attached here shows what the object looks like in the infrared spectrum, which can peer through obscuring dust.

Under visible light, everything just looks like a large black structure; only a little yellow light reveals that there might be stars forming inside. But when you look in the infrared spectrum, everything’s different. The young stars are the bright yellow dots near the middle of the image. The jets are wisps of green shooting out of them. As the jets extend, they cool down, transitioning to orange and then red at the end.

Astronomers believe the stars are giving off regular bursts of energy. The material closest to the stars is heated by the shockwaves from a recent stellar outburst. Other outbursts are further along the jet, getting cooler as they get more distant from the star.

Original Source: CfA News Release

April 30, 2007July 31, 2007 by Fraser Cain

Triple View of the Sombrero Galaxy

When we look into the skies with our eyes, we see in the visible spectrum. Although objects can look beautiful, it’s only a fraction of the entire electromagnetic spectrum. To really see and understand the Universe, you’ll want to look in different regions of the spectrum. The three great observatories: Hubble, Spitzer and Chandra, have teamed up to spotlight the Sombrero Galaxy (aka M104) in three different wavelengths.
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