Astronomers Discover Stars with Carbon Atmospheres

Astronomers at the University of Arizona have discovered a new class of white dwarfs, ones with carbon atmospheres. Most stars end their lives as white dwarfs (with only a few of them ending up exploding as supernovae). It is believed that most white dwarfs have cores consisting of oxygen and carbon which are obscured by the hydrogen and helium atmosphere surrounding them.

Recently however, astronomers have found stars with "no detectable traces of helium and hydrogen in their atmospheres" (Patrick Dufour). Dufour along with other astronomers at the University of Arizona believe that they may be seeing the bare cores of these white dwarfs. Found using the Sloan Digital Sky Survey (SDSS), white dwarfs such as these (which displayed carbon features) are dubbed DQ's (carbon white dwarfs). When observed via optical light, DQ white dwarf stars appear to be mostly carbon and helium. It is hypothesized that convection within the star causes carbon from the core to be dredged-up to the surface.

So far, eight carbon-dominated atmosphere DQ white dwarfs have been found among the 200 that Dufour and his team have searched. However, these stars lie at temperatures between 18,000 and 23,000 Kelvin, much hotter than what can be explained using the standard (convection/dredged-up) model for DQ white dwarfs. It is thought that these stars could be the next evolutionary step for stars such as H1504+65 (a hot pre-white dwarf star which is thought to have a surface of 50% carbon and 50% oxygen), which was discovered by John Nousek (of Pennsylvania State University), Leibert (of UA), and others. Currently, H1504+65 has a temperature of about 200,000 K; however, it is thought that when this star cools, it could become a pure-carbon star. The picture to the left is an artists conception of what the surface H1504+65 looks like.

For stars above 25,000 K, Dufour and his colleagues say that traces of helium rise up to the top of the star, which forms a thin layer and thus, disguises the star as a helium white dwarf. However, between the temperatures of 18,000 and 23,000 K, it is thought that convection dilutes the helium, the heavier oxygen sinks to the core, and the carbon is seen. It is also thought that a mass of nine to eleven solar masses could explain the carbon atmosphere white dwarfs found.

I think that this find is interesting because it could represent a new branch in stellar evolution. This could change the way we look at the formation and death of stars in the universe. The more unusual stars that are found, the more we can learn about stellar dynamics which are taking place now (and possibly about ones that occurred in the past).


http://uanews.org/node/17027

Scientists Discover Record Fifth Planet Orbiting Nearby Star

Astronomers have recently discovered a fifth planet around the star 55 Cancri. This star lies 41 light-years away (or 12.6 parsecs) towards the constellation of Cancer, the Crab. 55 Cancri is a binary star system with one star being a G-type star (the same as our sun) and the other being a red dwarf. The image to the right is an artists conception of what a planet around 55 Cancri might look like.

There are multiple methods for discovering extrasolar planets. The main methods for detection are astrometry, radial velocity (or doppler spectroscopy), pulsar timing, transits, gravitational microlensing, circumstellar disks, and direct imaging. The fifth star around 55 Cancri was discovered using the radial velocity method. In this method, one looks for doppler shifts in the spectrum of the star to determine whether or not there is an orbiting planet(s).

The planet, which was discovered by astronomers at San Francisco State University, University of California (Berkeley), and a team of other collaborators, is about 45 times the mass of the Earth and could be similar to Saturn (in terms of composition and appearance). It is the fourth planet from the star and has an orbital period of 260 days (or about .71 Earth years). Located in the habitable zone, a region of space where conditions are favorable for life, the planet lies 116.7 million kilometers (or .78 AU [where Earth is 1 AU away from the Sun]). The image to the left shows the 55 Cancri system on top and our own solar system (for comparison) on the bottom. The green areas in the pictures depict the location of the habitable zones in each system.

Thus far, all the planets discovered around 55 Cancri are gas giant-like planets ranging in size from Neptune to larger than Jupiter. These planets have nearly circular orbits with a Jupiter like planet orbiting at nearly the same distance as our Jupiter. These findings, along with others like them, leave hope for finding Earth-like planets around other stars and life elsewhere in the galaxy.

I think that finding planets around other stars is always a good thing. Finding more planets around stars allows us to get a better picture of how our own solar system formed and the evolution of solar systems in general.

NASA article:
http://www.jpl.nasa.gov/news/news.cfm?release=2007-128
Space.com article:
http://www.space.com/scienceastronomy/071106-five-planets.html

Hundreds of Missing Black Holes Found

A black hole is a region of space in which gravity is so strong that not even light can escape. Typical black holes range in size from stellar-mass black holes (which form mainly via the collapse of a massive star) to supermassive black holes which reside in the cores of galaxies. It is assumed that most galaxies contain a supermassive black hole at their core. Till recently, many black holes had been "missing." However, using both Spitzer (an infrared space telescope) and Chandra (an x-ray space telescope), a large fraction of these black holes have been found. The picture to the right is an artists conception of a growing black hole/quasar.

These black holes, due to their energetic nature, are considered quasars. A quasar or QUASi-stellAR radio source is a compact halo of matter surrounding a supermassive black hole within a young galaxy. These black holes/quasars were found within Milky Way mass galaxies of irregular shape at 9 to 11 billion light years away.


A team lead by Emanuele Daddi (of the Commissariat a l'Energie Atomique in France) studied 1,000 galaxies and found that, using Spitzer, 200 of those had an overabundance of infrared light. When studied with Chandra, the team found quasars within those 200 galaxies. The picture on the left shows an area of the sky containing galaxies with quasars in them (those galaxies are circled). This picture was taken using the Spitzer space telescope. It is thought that the quasars heat the dust surrounding them, thus giving off infrared light.

The finding of these new quasars has helped to change the way we think that massive galaxies evolve. It is now believed that the stars and black holes in massive galaxies form together until the black hole gets too massive, at which point it stops star formation. Additionally, in the past, it was believed that galaxy mergers played a large part in ignition of quasar activity, but seeing so many unscathed galaxies, it is now believed this is not true.

Finding so many new black holes in old galaxies will help us further refine our theories on galaxy/black hole formation in the early universe. This further knowledge can also aid us in our studies in the future. I also look forward to finding out what else Spitzer and Chandra can find and tell us about the universe.

NASA article:
http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20071025.html
Space.com article:
http://www.space.com/scienceastronomy/071025-missing-bholes.html

Cluster monitors convection cells over the polar caps

A European Space Agency (ESA) spacecraft named Cluster has recently helped to uncover important information regarding convection cells of matter found above the polar ice caps.

The Cluster mission, which is actually four spacecraft, launched in 2000, is designed to study small-scale plasma structures and processes.

A convection cell, which is a fluid dynamical phenomenon, occurs in situations where there are temperature difference within a liquid or gas. Cold gas or liquid moves underneath warmer liquid or gas, which then forces the warmer areas to rise and creates a cycle called convection (wherein the moving mass itself is called the convection cell). These convection cells, which are related to the Earth's magnetic field and the activities of the sun, were mapped with data collected for various solar conditions.












Normally, the Earth's magnetic field or magnetosphere, is stretched and compressed by the force of the solar wind (or charged particles emitted from the sun) as seen in the picture on the left. This magnetosphere deflects most of the particles, however, it can also allow the particles to pass through to the Earth's atmosphere. This action can create what is known as the aurora borealis or northern lights.

One method for studying the magnetosphere and convection cells is by looking at plasma at hundreds of kilometers above the Earth's poles. This region, called the high-latitude ionosphere, works well for studying these such convection cells and their interactions with the Earth and its magnetosphere.

After six years of collecting data, a full convection map has been created. Previously, partial maps have been produced via ground based observations from projects such as SuperDARN (Super Dual Aurora Radar Network), however, this is the first time a space based mission has made these maps (as seen below).


The map on the left is for the southward field and the one on the bottom right is for the northward field. As can be seen, the two maps differ in the number of convection cells seen.

These observations and future observations can be used to monitor coronal flares, coronal mass ejections and other such outbursts from the sun. This data can further be used to help safe guard astronauts and satellites in orbit above the Earth.















I think that it is interesting to see the different convection cell structures on the north and south poles and how changes in the sun affect the structures seen. It should be interesting to see what more data from the Cluster satellites can produce and what the effects of this research will be.


ESA article:
http://clusterlaunch.esa.int/science-e/www/object/index.cfm?fobjectid=41454
Space.com article:
http://www.space.com/scienceastronomy/071023-st-sun-earth-connection.html

Formation of life on earth

The question of how life formed on Earth is a much debated topic that is constantly undergoing revisions and modifications. It was once thought that all the material necessary for living beings to form was present on Earth; however, other hypothesis have been put forward. One such idea is called panspermia, or the idea that the seeds of life existed in the universe already and that life on Earth came about through this method.

Recently, a team of chemists at the University of Missouri-Columbia have created a new computer model which indicates that adenine (a chemical component of DNA) can form and exist out in space. The team believes that if adenine can be found in meteorites and elsewhere in the solar system, that it is possible for it to be found in interstellar space.

The computer simulation consisted of HCN (hydrogen cyanide [which already exists in interstellar clouds]) in the cold vacuum of space and showed, that with a small energy boost, molecules of adenine can begin forming.

With this discovery, it is possible that astronomers and biologists will have to rethink just how life was formed on Earth and how it can be formed elsewhere in the galaxy and universe. Personally, I am excited at the prospect of learning more about the formation of life on this earth and elsewhere in the universe. I think it would be amazing if we could find other forms of life (or the remains of past life) here in our own solar system. This type of research can only help to further our knowledge and understanding how things form and work within the universe.

The full article can be found at:
http://www.space.com/scienceastronomy/070911_st_adenine_dust.html

first post!

To all who are concerned, this is my astroblog (at the moment at least)...so enjoy!