The Formax Galaxy

The center of the Fornax galaxy cluster is shown in this Chandra image. The galaxy NGC 1404 is shown below and to the left of the center. Hot gas is clearly visible in the center of the cluster and around NGC 1404. (Credit: NASA/CXC/Columbia U./C.Scharf et al.)


Using data from NASA's Chandra X-ray Observatory, scientists have reported the possible detection of a binary star system that was later destroyed in a supernova explosion. The new method they used provides great future promise for finding the detailed origin of these important cosmic events.

In an article on the February 14th issue of the journal Nature, Rasmus Voss of the Max Planck Institute for Extraterrestrial Physics in Germany and Gijs Nelemans of Radboud University in the Netherlands searched Chandra images for evidence of a much sought after, but as yet unobserved binary system - one that was about to go supernova. Near the position of a recently detected supernova, they discovered an object in Chandra images taken more than four years before the explosion.

The supernova, known as SN 2007on, was identified as a Type Ia supernova. Astronomers generally agree that Type Ia supernovas are produced by the explosion of a white dwarf star in a binary star system. However, the exact configuration and trigger for the explosion is unclear. Is the explosion caused by a collision between two white dwarfs, or because a white dwarf became unstable by pulling too much material off a companion star?
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Answering such questions is a high priority because Type Ia supernovas are major sources of iron in the Universe. Also, because of their nearly uniform intrinsic brightness, Type Ia supernova are used as important tools by scientists to study the nature of dark energy and other cosmological issues.

"Right now these supernovas are used as black boxes to measure distances and derive the rate of expansion of the universe," said Nelemans. "What we're trying to do is look inside the box."

If the supernova explosion is caused by material being pulled off a companion star onto the white dwarf, fusion of this material on the surface of the star should heat the star and produce a strong source of X-radiation prior to the explosion. Once the supernova explosion occurs, the white dwarf is expected to be completely destroyed and then would be undetectable in X-rays. In the merger scenario, the intensity of X-ray emission prior to the explosion is expected to be much weaker.

Based on the detection of a fairly strong X-ray source at approximately the position of SN 2007on 4 years before the explosion, Voss and Nelemans conclude that the data support the scenario where matter is pulled off a companion star. The small number of X-ray sources in the field implies that there is only a small chance of an unrelated source being so close by coincidence. Also, the X-ray source has similar properties to those expected for fusion on a white dwarf, unlike most X-ray sources in the sky.

However, in follow-up studies, Voss, Nelemans and colleagues Gijs Roelofs (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.) and Cees Bassa (McGill University, Canada) used higher-quality optical images to better determine the supernova's position. This work, which is not yet published, shows a small, but significant difference in the measured positions of the supernova and the X-ray source, suggesting the source may not be the progenitor.

Follow-up Chandra observations hint that the X-ray object has disappeared, but further observations are needed to finally decide whether the source was the progenitor or not.

The team is also applying this new method to other supernovas and has high hopes that they will eventually succeed in identifying the elusive cause of at least some of these explosions.

"We're very excited about opening up a new way of studying supernovas, even though we're not sure that we've seen this particular stellar bomb before it exploded," said Gijs Roelofs. "We're very confident that we'll learn a lot more about these important supernovas in the future."

Voss agrees that, even if the X-ray source is not found to be the progenitor of SN 2007on, the hunt is worth the effort.

"Finding the progenitor to one of these Type Ia supernovas is a great chase in astronomy right now," he said. "These supernovas are great tools for studying dark energy, but if we knew more about how they form they might become even better tools."

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White Dwarfs Get A Kick

NGC 6397. Click on Image to Enlarge

These images show young and old white dwarf stars — the burned-out relics of normal stars — in the ancient globular star cluster NGC 6397.

The image at left, taken by a ground-based telescope, shows the dense swarm of hundreds of thousands of stars that make up the globular cluster. The white box outlines the location of the observations made by NASA's Hubble Space Telescope.

The image at top, right, taken by Hubble's Advanced Camera for Surveys, reveals young white dwarfs less than 800 million years old and older white dwarfs between 1.4 and 3.5 billion years old. The photo shows 12 of the 84 white dwarfs in the Hubble study. The blue squares pinpoint the young white dwarfs; the red circles outline the older white dwarfs. The Hubble researchers distinguished the younger from the older white dwarfs based on their colour and brightness. The younger white dwarfs are hotter and therefore bluer and brighter than the older ones.

The astronomers were surprised to find young white dwarfs far away from the cluster's core. They had assumed that the youngsters would reside at the center and migrate over time to the cluster's outskirts. The astronomers proposed that the cluster stars that burn out as white dwarfs are given a boost that propels them to the edge of the cluster.

Close-up images of the white dwarfs are shown at bottom, right. The blue boxes represent the young white dwarfs; the red boxes indicate the older white dwarfs.

Read more @ How White Dwarfs Get Their 'Kicks' from Hubble
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White Dwarfs Rocket Away When They're Born @ Universe Today
First Findings On Key Astrophysics Problem - from Science Daily
Radiation Flashes May Help Crack Cosmic Mystery from Science Daily
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Star Streaks Across The Sky

A new ultraviolet mosaic from NASA's Galaxy Evolution Explorer shows an amazingly long comet-like tail behind a star streaking through space at supersonic speeds. The star, named Mira after the Latin word for "wonderful," has been a favorite of astronomers for about 400 years. It is a fast-moving, older star called a red giant that sheds massive amounts of surface material.

The space-based Galaxy Evolution Explorer scanned the popular star during its ongoing survey of the entire sky in ultraviolet light. Astronomers then noticed what looked like a comet with a tail. In fact, material blowing off Mira is forming a wake 13 light-years long, or about 20,000 times the average distance of Pluto from the sun. Nothing like this has ever been seen before around a star.

As Mira hurtles along, its tail sheds carbon, oxygen and other important elements needed for new stars, planets and possibly even life to form. This tail material, visible now for the first time, has been released over the past 30,000 years.
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Billions of years ago, Mira was similar to our sun. Over time, it began to swell into what's called a variable red giant - a pulsating, puffed-up star that periodically grows bright enough to see with the naked eye. Mira will eventually eject all of its remaining gas into space, forming a colorful shell called a planetary nebula. The nebula will fade with time, leaving only the burnt-out core of the original star, which will then be called a white dwarf.

Compared to other red giants, Mira is traveling unusually fast, possibly due to gravitational boosts from other passing stars over time. It now plows along at 130 kilometers per second, or 291,000 miles per hour. Racing along with Mira is a small, distant companion thought to be a white dwarf. The pair, also known as Mira A (the red giant) and Mira B, orbit slowly around each other as they travel together in the constellation Cetus 350 light-years from Earth.

In addition to Mira's tail, Galex also discovered a bow shock, a type of buildup of hot gas, in front of the star, and two sinuous streams of material coming out of the star's front and back. Astronomers think hot gas in the bow shock is heating up the gas blowing off the star, causing it to fluoresce with ultraviolet light. This glowing material then swirls around behind the star, creating a turbulent, tail-like wake. The process is similar to a speeding boat leaving a choppy wake, or a steam train producing a trail of smoke.

The fact that Mira's tail only glows with ultraviolet light might explain why other telescopes have missed it. The Galaxy Evolution Explorer is very sensitive to ultraviolet light and also has an extremely wide field of view, allowing it to scan the sky for unusual ultraviolet activity.

Mira's tail offers a unique opportunity to study how stars like our sun die and ultimately seed new solar systems.

"It's amazing to discover such a startlingly large and important feature of an object that has been known and studied for over 400 years," said James D. Neill of Caltech. "This is exactly the kind of surprise that comes from a survey mission like the Galaxy Evolution Explorer."

"This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved," said Mark Seibert of the Observatories of the Carnegie Institution of Washington in Pasadena. "We hope to be able to read Mira's tail like a ticker tape to learn about the star's life."

Mira is also what's called a pulsating variable star. It dims and brightens by a factor of 1,500 every 332 days, and will become bright enough to see with the naked eye in mid-November 2007. Because it was the first variable star with a regular period ever discovered, other stars of this type are often referred to as "Miras."

Mira is located 350 light-years from Earth in the constellation Cetus, otherwise known as the whale. Coincidentally, Mira and its "whale of a tail" can be found in the tail of the whale constellation.

Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory, also in Pasadena, manages the mission and built the science instrument. Caltech manages JPL for NASA. The mission was developed under NASA's Explorers Program managed by NASA's Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission.

Speeding-Bullet Star Leaves Enormous Streak Across Sky JPL News Release
Graphics & information about the Galaxy Evolution Explorer are online at
http://www.nasa.gov/galex - and - http://www.galex.caltech.edu.
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Mira: Star with a Comet-like Tail from Centauri Dreams
Shocking Mira and Bowshocks by Julianne @ Cosmic Variance
Mira's Supersonic Comet Tail Across The Sky @ Scientific Blogging
Star light, star bright: - FSU duplicating conditions of supernovas.

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