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In the news this month: solar flares as activity increases is solar cycle 24

Sunspot 1158
Sunspot 1158 CREDIT: Karzaman Ahmad, Langkawi National Observatory, Malaysia
After a prolonged period of very little activity, the Sun produced the first X-class flare of solar cycle 24 during February. X-class flares are the most powerful solar events, producing X-rays and sending large amounts of charged particles out into space in what is known as a coronal mass ejection, or CME. Originating from a spot on the Sun's surface known as Active Region 1158, a region wider than Jupiter containing several sunspots, this particular eruption (the strongest in four years) peaked at 0156 UT on February 15th and resulted in a CME heading in our direction, producing some good displays of aurora at high latitudes a few days later. On February 18th, sunspot complex 1161-1162 also erupted, sending a further significant CME in the Earth's direction. Now that the Sun's activity is starting to increase again, it is worth taking a look, but make sure that if you do observe the Sun, you do it safely. NEVER point a telescope or binoculars at the Sun.

This blog post is a news story from the Jodcast, aired in the March 2011 edition.

Posted by Megan on Wednesday 02nd Mar 2011 (06:40 UTC) | Add a comment | Permalink

In the news this month: seasonal changes in the northern dunes of Mars

Polar sand dunes from HiRISE
Polar dunes made of basalt and gypsum grains in the northan polar region of Mars. CREDIT: NASA/JPL/University of Arizona
While the planet Mars is home to the largest volcano in the solar system, and the enormous Mariner Valley which cuts through a huge region of the planet's surface, the crust of the planet is today fairly inactive. Unlike the Earth, where plate tectonics cause the continents to move and ever-so-slowly collide with each other, Mars today has no such large-scale geological activity. But that doesn't mean the surface never changes with time.

Several spacecraft have been imaging the surface of the red planet over many years, some at very high resolution, and the images sent back are showing an amazing amount of surface change on short timescales. In 2010, images released from the High-Resolution Imaging Science Experiment on the Mars Reconnaissance Orbiter showed evidence of avalanches on sand dunes first imaged by Mariner 9 in the 1970s located in the northern polar region. Most older images of the region suggested that it was mostly stable with very little variation over time, but last year's images from the MRO show clear evidence of sediment transport with one image even catching a dust cloud kicked up by an avalanche. Now, a team led by Candice Hansen at the Planetary Science Institute in Arizona in the USA, have analysed the images and determined the cause of the avalanches.

The team found that numerous dunes in the northern polar region showed evidence of morphological changes over the course of a Martian year. Seasonal variations have been seen in images from previous Martian orbiters, but this is the first time they have been seen in such detail that the underlying processes can be studied. Some of the physical processes causing the changes are the same as those seen on sand dunes here on the Earth, but on Mars there is an additional process not found on the Earth.

The Earth's polar caps are made of ice, but the atmosphere of Mars has a very high percentage of carbon dioxide, a gas which freezes in the cold temperatures of the Martian winter and settles on the surface. In the Martian spring, the carbon dioxide ice sublimates, turning back into a gas and returning to the atmosphere. This sublimation process can destabilise the dunes, especially at the top where more sunlight is received and the side of the dune is steepest, causing loosened sand to cascade down the side of the dunes, creating gullies and aprons of material.

Over the area studied, a dune field 6.4- by 19.2-km in size, roughly twenty per cent of the dunes showed measurable changes over one Martian year and another twenty per cent showed slight changes. The widespread nature of these variations and the pristine appearance of the dunes suggests that sand transport on the surface is an active and ongoing process. Similar image comparisons of dunes at lower latitudes further from the polar regions show no changes in dune shape over the same period, adding to the evidence that the observed changes at high latitude require carbon dioxide ice.

This blog post is a news story from the Jodcast, aired in the March 2011 edition.

Hansen CJ, Bourke M, Bridges NT, Byrne S, Colon C, Diniega S, Dundas C, Herkenhoff K, McEwen A, Mellon M, Portyankina G, & Thomas N (2011). Seasonal erosion and restoration of Mars' northern polar dunes. Science (New York, N.Y.), 331 (6017), 575-8 PMID: 21292976

Posted by Megan on Wednesday 02nd Mar 2011 (06:25 UTC) | Add a comment | Permalink

In the news this month: giant black hole in a dwarf galaxy

The dwarf starburst Henize 2-10
Composite image of the dwarf galaxy Henize 2-10. Hubble Space Telescope data is colored red, green and blue, Very Large Array data is yellow and the Chandra X-Ray Observatory data is purple. CREDIT: Reines, et al., NRAO/AUI/NSF, NASA
Normal massive galaxies contain supermassive black holes in their central bulges. Observations have shown evidence for such objects in pretty much all massive Milky Way-like galaxies, as well as large elliptical galaxies. But not all galaxies are as large as the Milky Way. Many dwarf galaxies are known in the nearby universe, usually irregular in shape and often forming stars much faster than galaxies like our own. Now, a team of astronomers, led by Amy Reines at the University of Virginia, have found evidence for a supermassive black hole in the centre of one of these dwarf irregular galaxies.

The galaxy, known as Henize 2-10, is a small galaxy located some 30 million light years away in the southern constellation of Pyxis. It is classified as a blue compact dwarf and is highly irregular in shape. Despite being similar in mass to the Large Magellanic Cloud, Henize 2-10 is forming stars some ten times faster.

The team observed the galaxy with a number of telescopes operating in different parts of the electromagnetic spectrum as part of a survey of several galaxies. When they looked at data taken with the Very Large Array, a collection of radio telescopes situated in New Mexico in the USA, they found a small object at the centre of the galaxy which was very bright at radio wavelengths. When they looked with the Hubble Space Telescope they found that the object was not a large cluster of stars, several of which exist in other parts of Henize 2-10, but data from the archive of the Chandra X-ray telescope showed that there was a source of X-rays at the same position. The amount of energy being emitted by this object in different parts of the spectrum is consistent with it being a supermassive black hole with a mass estimated to be roughly two million times that of the Sun.

This is an exciting but unexpected result, since few dwarf galaxies are known to contain supermassive black holes, and those that do are forming stars far more slowly than Henize 2-10, and there is evidence that the black hole is growing by actively consuming material from the surrounding galaxy. This discovery has implications for our understanding of the growth of galaxies in the early universe, since the properties of Henize 2-10 (it's active black hole and simultaneous rapid star formation) resemble those of low-mass high-redshift galaxies seen in the distant universe when the early stages of galaxy assembly and evolution were happening on a large scale.

This blog post is a news story from the Jodcast, aired in the March 2011 edition.

Reines, A., Sivakoff, G., Johnson, K., & Brogan, C. (2011). An actively accreting massive black hole in the dwarf starburst galaxy Henize‚ÄČ2-10 Nature, 470 (7332), 66-68 DOI: 10.1038/nature09724

Posted by Megan on Wednesday 02nd Mar 2011 (05:59 UTC) | Add a comment | Permalink

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