Eagle Nebula by Piotr Wachowicz
The Horsehead and the Flame Nebulas in the constellation Orion
It is a large group of old stars that are closely packed in a symmetrical, somewhat spherical form. Globular clusters, so called because of their roughly spherical appearance, are the largest and most massive star clusters.
The globular clusters in the Milky Way are all estimated to be at least 10 billion years old and therefore contain some of the oldest stars in the galaxy.
[The graphic shows habitable zone distances around various types of stars. Some of the known extrasolar planets that are considered to be in the habitable zone of their stars are also shown. On this scale, Earth-Sun distance is one astronomical unit, which is roughly 150 million kilometers. Click on the image for a higher resolution version. Credit: Chester Herman]
“Researchers searching the galaxy for planets that could pass the litmus test of sustaining water-based life must find whether those planets fall in a habitable zone, where they could be capable of having liquid water and sustaining life. New work, led by a team of Penn State researchers, will help scientists in that search.
Using the latest data, the Penn State Department of Geosciences team has developed an updated model for determining whether discovered planets fall within a habitable zone. The work builds on a prior model by James Kasting, Evan Pugh Professor of Geosciences at Penn State, to offer a more precise calculation of where habitable zones around a star can be found.
Comparing the new estimates with the previous model, the team found that habitable zones are actually farther away from the stars than previously thought.
“This has implications for finding other planets with life on them,” said post-doctoral researcher Ravi kumar Kopparapu, a lead investigator on the study, which will be published described in Astrophysical Journal.
For the paper, Kopparapu and graduate student Ramses Ramirez used updated absorption databases of greenhouse gases (HITRAN and HITEMP). The databases have more accurate information on water and carbon dioxide than previously was available and allowed the research team to build new estimates from the groundbreaking model Kasting created 20 years ago for other stars.”
This movie is made up of several observations taken by the Chandra X-Ray Observatory, showing a stream of energetic particles being blown from a pulsar (a fast rotating neutron star). The jet seen here is around 0.7 light years long, and the jet of particles creating it are spat out at 70% of the speed of light. It appears to be helix-shaped, which suggests that the star’s magnetic poles aren’t perfectly aligned with its axis of rotation – the first time this has been observed in such an object. The neutron star itself is the small whitish blog in the very centre of that disk-like structure.
The Vela Pulsar is only about 12 km in diameter, but is more massive than the Sun. It rotates once ever 89 milliseconds, which is faster than the blades of a helicopterThe supernova which created it gave it an immense kick which caused it to be travelling through space at 1200 kilometres per second!
The gas looks like a face
Zeta Ophiuchus, a massive star plowing through the gas and dust floating in space. Zeta Oph is a bruiser, with 20 times the Sun’s mass. It’s an incredibly luminous star, blasting out light at a rate 80,000 times higher than the Sun! Even at its distance of 400 light years or so, it should be one of the brightest stars in the sky … yet it actually appears relatively dim to the eye.
That’s because it’s sitting in a dust cloud, dense opaque material that absorbs the light from the mighty star and diminishes it. However, infrared light can penetrate the murk, allowing us to peer into the cloud and see what’s going on.
Zeta Oph is blasting out a fierce wind of subatomic particles (think of it as a super-solar wind) that expands around the star. Not only that, but the star itself is moving rapidly through the dust at a speed of about 25 kilometers per second (15 miles per second), so it’s violently compressing the material ahead of it. This creates that wave structure, which is similar to the wave off the bow of a boat, though more like the supersonic shock wave generated as a fighter jet screams through the air.
That curving wave is roughly four light years long: That’s 40 trillion kilometers!
Violent Birth of Supernovae |
A team of astronomers led by the University of Leicester has uncovered new evidence that suggests that X-ray detectors in space could be the first to witness new supernovae that signal the death of massive stars.
Astronomers have measured an excess of X-ray radiation in the first few minutes of collapsing massive stars, which may be the signature of the supernova shock wave first escaping from the star.
The findings have come as a surprise to Dr Rhaana Starling, of the University of Leicester Department of Physics and Astronomy whose research is published in the Monthly Notices of the Royal Astronomical Society.
Dr Starling said: “The most massive stars can be tens to a hundred times larger than the Sun. When one of these giants runs out of hydrogen gas it collapses catastrophically and explodes as a supernova, blowing off its outer layers which enrich the Universe. But this is no ordinary supernova; in the explosion narrowly confined streams of material are forced out of the poles of the star at almost the speed of light. These so-called relativistic jets give rise to brief flashes of energetic gamma-radiation called gamma-ray bursts, which are picked up by monitoring instruments in Space, that in turn alert astronomers.”
Gamma-ray bursts are known to arise in stellar deaths because coincident supernovae are seen with ground-based optical telescopes about ten to twenty days after the high energy flash. The true moment of birth of a supernova, when the star’s surface reacts to the core collapse, often termed the supernova shock breakout, is missed. Only the most energetic supernovae go hand-in-hand with gamma-ray bursts, but for this sub-class it may be possible to identify X-ray emission signatures of the supernova in its infancy. If the supernova could be detected earlier, by using the X-ray early warning system, astronomers could monitor the event as it happens and pinpoint the drivers behind one of the most violent events in our Universe. continue reading
Page 1 of 4