Sunspot 1748 Makes it's Presence Known: Video

Sunspot 1748 had just begun its rotation to the Earthside of the Sun on April 5th and already has erupted twice. The first was a C2-class flare and a stronger M2-class flare occurred about 10 hours later. 

Credit: NASA / SDO /

Youngest-Known Supernova Remnants in the Milky Way Galaxy

G306.3–0.9 in context with star-formation regions in southern Centaurus. Chandra X-ray observations (blue), Spitzer infrared data (red, cyan), and radio observations (purple) from the Australia Telescope Compact Array are merged in this composite.

The image is one degree across, which corresponds to 450 light-years at the remnant's estimated distance. 

Credit: X-ray: NASA/CXC/Univ. of Michigan/M. Reynolds et al; Infrared: NASA/JPL-Caltech; Radio: CSIRO/ATNF/ATCA

While performing an extensive X-ray survey of our galaxy's central regions, NASA's Swift satellite has uncovered the previously unknown remains of a shattered star. The full report here and at NASA Goddard

Designated G306.3-0.9 after the coordinates of its sky position, the new object ranks among the youngest-known supernova remnants in our Milky Way galaxy.

"Astronomers have previously cataloged more than 300 supernova remnants in the galaxy," said lead scientist Mark Reynolds, a postdoctoral researcher at the University of Michigan in Ann Arbor.

"Our analysis indicates that G306.3-0.9 is likely less than 2,500 years old, making it one of the 20 youngest remnants identified."

Astronomers estimate that a supernova explosion occurs once or twice a century in the Milky Way.

The expanding blast wave and hot stellar debris slowly dissipate over hundreds of thousands of years, eventually mixing with and becoming indistinguishable from interstellar gas.

Like fresh evidence at a crime scene, young supernova remnants give astronomers the best opportunity for understanding the nature of the original star and the details of its demise.

Supernova remnants emit energy across the electromagnetic spectrum, from radio to gamma rays, and important clues can be found in each energy band.

X-ray observations figure prominently in revealing the motion of the expanding debris, its chemical content, and its interaction with the interstellar environment, but supernova remnants fade out in X-ray light after 10,000 years.

Indeed, only half of those known in the Milky Way galaxy have been detected in X-rays at all.

Reynolds leads the Swift Galactic Plane Survey, a project to image a two-degree-wide strip along the Milky Way's central plane at X-ray and ultraviolet energies at the same time. Imaging began in 2011 and is expected to complete this summer.

"The Swift survey leverages infrared imaging previously compiled by NASA's Spitzer Space Telescope and extends it into higher energies," said team member Michael Siegel, a research associate at the Swift Mission Operations Center (MOC) in State College, Pa., which is operated by Penn State University.

"The infrared and X-ray surveys complement each other because light at these energies penetrates dust clouds in the galactic plane, while the ultraviolet is largely extinguished."

On Feb. 22, 2011, Swift imaged a survey field near the southern border of the constellation Centaurus.

Although nothing unusual appeared in the ultraviolet exposure, the X-ray image revealed an extended, semi-circular source reminiscent of a supernova remnant.

A search of archival data revealed counterparts in Spitzer infrared imagery and in radio data from the Molonglo Observatory Synthesis Telescope in Australia.

To further investigate the object, the team followed up with an 83-minute exposure using NASA's Chandra X-ray Observatory and additional radio observations from the Australia Telescope Compact Array (ATCA), located near the town of Narrabri in New South Wales.

"The fantastic sensitivity of ATCA has enabled us to image what, at radio wavelengths, turns out to be the dimmest remnant we have ever seen in our galaxy," said team member Cleo Loi, an undergraduate student at the University of Sydney who led the analysis of the radio observations.

A paper describing the team's findings will appear in an upcoming edition of The Astrophysical Journal and was published online on Friday.

Using an estimated distance of 26,000 light-years for G306.3-0.9, the scientists determined that the explosion's shock wave is racing through space at about 1.5 million mph (2.4 million km/h).

The Chandra observations reveal the presence of iron, neon, silicon and sulfur at temperatures exceeding 50 million degrees F (28 million C), a reminder not only of the energies involved but of the role supernovae play in seeding the galaxy with heavy elements produced in the hearts of massive stars.

"We don't yet have enough information to determine what type of supernova this was and therefore what type of star exploded, but we've planned a further Chandra observation to improve the picture," said coauthor Jamie Kennea, also a researcher at the Swift MOC.

"We see no compelling evidence that the explosion formed a neutron star, and this is something we hope can be determined one way or the other by future work."

Methuselah: Oldest Known Star HD 140283

Credit: Digitized Sky Survey (DSS), STScI/AURA, Palomar/Caltech, and UKSTU/AAO

This Digitized Sky Survey image shows the oldest star with a well-determined age in our galaxy. Called the Methuselah star, HD 140283 is 190.1 light-years away. 

Astronomers refined the star's age to about 14.5 billion years (which is older than the universe), plus or minus 800 million years. 

Image released March 7, 2013.

Because the aging star is relatively nearby, familiar stars and constellations as seen from Earth are in the sky, but in different locations, as seen in this annotated view.

At upper left is the constellation Orion, which looks distorted from our new perspective in space. 

Just to the upper left of the foreground star is the Pleiades cluster. 

To the lower left of the cluster, our Sun has dimmed to an apparent magnitude of +7, placing it below naked-eye visibility.

Russian Meteor Impact: What is known? Technical Details

The large fireball (technically, a "superbolide") observed on the morning of February 15, 2013 in the skies near Chelyabinsk, Russia, was caused by a relatively small asteroid approximately 17 to 20 meters in size, entering the Earth's atmosphere at high speed and a shallow angle.

In doing so it released a tremendous amount of energy, fragmented at high altitude, and produced a shower of pieces of various sizes that fell to the ground as meteorites.

The fireball was observed not only by video cameras and low frequency infra-sound detectors, but also by U.S. Government sensors.

As a result, the details of the impact have become clearer. There is no connection between the Russian fireball event and the close approach of asteroid 2012 DA14, which occurred just over 16 hours later.

New Fireball Data
U.S. Government sensor data on fireballs are now reported on the NASA Near-Earth Object Program Office website.

The February 15th event is the first entry on this new site, and it provides the following information about the fireball:

• Date and time of maximum brightness: 15 Feb. 2013/03:20:33 GMT
• Geographic location of maximum brightness: Latitude: 54.8 deg. N :: Longitude: 61.1 deg. E
• Altitude of maximum brightness: 23.3 km (14.5 miles)
• Velocity at peak brightness: 18.6 km/s (11.6 miles/s)
• Approximate total radiated energy of fireball: 3.75 x 10^14 Joules. This is the equivalent of about 90 kilotons (kt) of TNT explosives, but it does not represent the total impact energy (see note below).
• Approximate total impact energy of the fireball in kilotons of TNT explosives (the energy parameter usually quoted for a fireball): 440 kt.

Note that the total energy of a fireball event is several times larger than the observed total radiated energy.

The JPL fireballs website uses the following empirical formula derived by Peter Brown and colleagues to convert the optical radiant energy Eo into an estimate of the total impact energy E (see: Brown et al., The flux of small near-Earth objects colliding with the Earth. Nature, vol. 420, 21 Nov. 2002, pp. 294-296):.

E = 8.2508 x E_o ^0.885

During the atmospheric entry phase, an impacting object is both slowed and heated by atmospheric friction.

In front of it, a bow shock develops where atmospheric gases are compressed and heated. Some of this energy is radiated to the object causing it to ablate, and in most cases, to break apart.

Fragmentation increases the amount of atmosphere intercepted and so enhances ablation and atmospheric braking.

The object catastrophically disrupts when the force from the unequal pressures on the front and back sides exceeds its tensile strength.

This was an extraordinarily large fireball, the most energetic impact event recognized since the 1908 Tunguska blast in Russian Siberia.

The meteorites recovered from the Chelyabinsk fireball are reported to be ordinary chondrites, which have a typical density of about 3.6 g/cm^3.

Given the total energy of about 440 kt, the approximate effective diameter of the asteroid would be about 18 meters, and its mass would be roughly 11,000 tons.

NB: All estimates of total energy, diameter and mass are very approximate.