VVV BD001

This image, from ESO’s VISTA telescope, shows a newly-discovered brown dwarf nicknamed VVV BD001, which is located at the very centre of this image. It is the first new brown dwarf spotted in our cosmic neighbourhood as part of the VVV Survey. VVV BD001 is located about 55 light-years away from us, towards the very crowded centre of our galaxy.

Brown dwarfs are stars that never quite managed to grow up into a star like our Sun. They are often referred to as “failed stars”; they are larger in size than planets like Jupiter, but smaller than stars.

This dwarf is peculiar in two ways; firstly, it is the first one found towards the centre of our Milky Way, one of the most crowded regions of the sky. Secondly, it belongs to an unusual class of stars known as “unusually blue brown dwarfs” — it is still unclear why these stars are bluer than expected.

Brown dwarfs are born in the same way as stars, but do not have enough mass to trigger the burning of hydrogen to become normal stars. Because of this they are much cooler and produce far less light, making them harder to find. Astronomers generally look for these objects using near and mid-infrared cameras and special telescopes that are sensitive to these very cool objects, but usually avoid looking in very crowded regions of space — such as the central region of our galaxy, for example.

VISTA (the Visible and Infrared Survey Telescope for Astronomy) is the world’s largest survey telescope and is located at ESO’s Paranal Observatory in Chile. It is performing six separate surveys of the sky, and the VVV (VISTA Variables in the Via Lactea) survey is designed to catalogue a billion objects in the centre of our own Milky Way galaxy. VVV BD001 was discovered by chance during this survey.

Scientists have used the VVV catalogue to create a 3 dimensional map of the central bulge of the Milky Way. The data have also been used to create a monumental 108 200 by 81 500 pixel colour image containing nearly nine billion pixels, one of the biggest astronomical images ever produced.

Image Credit: ESO, and D. Minniti and J. C. Beamín
Explanation from: https://www.eso.org/public/images/potw1338a/

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Comet ISON

This view of Comet C/2012 S1 (ISON) was taken with the TRAPPIST–South national telescope at ESO's La Silla Observatory on the morning of Friday 15 November 2013. Comet ISON was first spotted in our skies in September 2012, and will make its closest approach to the Sun in late November 2013.

TRAPPIST–South has been monitoring comet ISON since mid-October, using broad-band filters like those used in this image. It has also been using special narrow-band filters which isolate the emission of various gases, allowing astronomers to count how many molecules of each type are released by the comet.

Comet ISON was fairly quiet until 1 November 2013, when a first outburst doubled the amount of gas emitted by the comet. On 13 November, just before this image was taken, a second giant outburst shook the comet, increasing its activity by a factor of ten. It is now bright enough to be seen with a good pair of binoculars from a dark site, in the morning skies towards the East. Over the past couple of nights, the comet has stabilised at its new level of activity.

These outbursts were caused by the intense heat of the Sun reaching ice in the tiny nucleus of the comet as it zooms toward the Sun, causing the ice to sublimate and throwing large amounts of dust and gas into space. By the time ISON makes its closest approach to the Sun on 28 November (at only 1.2 million kilometres from its surface — just a little less than the diameter of the Sun!), the heat will cause even more ice to sublimate. However, it could also break the whole nucleus down into small fragments, which would completely evaporate by the time the comet moves away from the Sun's intense heat. If ISON survives its passage near the Sun, it could then become spectacularly bright in the morning sky.

The image is a composite of four different 30-second exposures through blue, green, red, and near-infrared filters. As the comet moved in front of the background stars, these appear as multiple coloured dots.

TRAPPIST–South (TRAnsiting Planets and PlanetesImals Small Telescope–South) is devoted to the study of planetary systems through two approaches: the detection and characterisation of planets located outside the Solar System (exoplanets), and the study of comets orbiting around the Sun. The 60-cm national telescope is operated from a control room in Liège, Belgium, 12 000 km away.

Image Credit: TRAPPIST/E. Jehin/ESO
Explanation from: https://www.eso.org/public/images/potw1346a/

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Saturn's F Ring

When seen up close, the F ring of Saturn resolves into multiple dusty strands. This Cassini view shows three bright strands and a very faint fourth strand off to the right.

The central strand is the core of the F ring. The other strands are not independent at all, but are actually sections of long spirals of material that wrap around Saturn. The material in the spirals was likely knocked out from the F ring's core during interactions with a small moon.

This view looks toward the unilluminated side of the rings from about 38 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on December 18, 2016.

The view was acquired at a distance of approximately 122,000 miles (197,000 kilometers) from Saturn and at a Sun-Ring-spacecraft, or phase, angle of 47 degrees. Image scale is 0.7 miles (1.2 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA20519

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Sun Emitted Trio of Solar Flares

NASA's Solar Dynamics Observatory captured this image of a solar flare peaking at 4:02 a.m. EDT on April 2, 2017, as seen in the bright flash near the Sun’s upper right edge. The image shows a subset of extreme ultraviolet light that highlights the extremely hot material in flares and which is typically colorized in blue.

NASA's Solar Dynamics Observatory captured this image of a solar flare peaking at 4:33 p.m. EDT on April 2, 2017, as seen in the bright flash near the Sun’s upper right edge. The image shows a subset of extreme ultraviolet light that highlights the extremely hot material in flares and which is typically colorized in blue.

NASA's Solar Dynamics Observatory captured this image of a solar flare peaking at 10:29 a.m. EDT on April 3, 2017, as seen in the bright flash near the Sun’s upper right edge. The image shows a subset of extreme ultraviolet light that highlights the extremely hot material in flares and which is typically colorized in teal.

The Sun emitted a trio of mid-level solar flares on April 2-3, 2017. The first peaked at 4:02 a.m. EDT on April 2, the second peaked at 4:33 p.m. EDT on April 2, and the third peaked at 10:29 a.m. EDT on April 3. NASA’s Solar Dynamics Observatory, which watches the Sun constantly, captured images of the three events. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel.

The first April 2 flare was classified as an M5.3 flare, while the second April 2 was an M5.7 flare. The April 3 flare was classified as an M5.8 flare. M-class flares are a tenth the size of the most intense flares, the X-class flares. The number provides more information about its strength. An M2 is twice as intense as an M1, an M3 is three times as intense, etc.

Image Credit: NASA/SDO
Explanation from: https://www.nasa.gov/feature/goddard/2017/nasa-s-solar-dynamics-observatory-captured-trio-of-solar-flares-april-2-3

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Mysterious flash of X-rays: Chandra Deep Field South X-ray Transient 1

• A mysterious X-ray source became 1,000 times brighter over a few hours before fading dramatically in about a day.

• This source was discovered in Chandra Deep Field-South data, giving the deepest X-ray image ever made.

• Hubble and Spitzer data indicate this source is likely located in a small galaxy about 10.7 billion light years from Earth.

• Evidence points to this being some sort of destructive event but perhaps unlike any ever seen before.

Scientists have discovered a mysterious flash of X-rays using NASA's Chandra X-ray Observatory, in the deepest X-ray image ever obtained. The X-ray source is located in a region of the sky known as the Chandra Deep Field-South (CDF-S), which is shown in the main panel of this graphic. Over the 17 years Chandra has been operating, the telescope has observed this field many times, resulting in a total exposure time of 7 million seconds, equal to two and a half months. In this CDF-S image, the colors represent different bands of X-ray energy, where red, green, and blue show the low, medium, and high-energy X-rays that Chandra can detect.

 

The mysterious source that scientists discovered, shown in the inset box, has remarkable properties. Prior to October 2014, this source was not detected in X-rays, but then it erupted and became at least a factor of 1,000 brighter in a few hours. After about a day, the source had faded completely below the sensitivity of Chandra.

Thousands of hours of legacy data from the Hubble and Spitzer Space Telescopes helped determine that the event came from a faint, small galaxy about 10.7 billion light years from Earth. For a few minutes, the X-ray source produced a thousand times more energy than all the stars in this galaxy.

While scientists think this source likely comes from some sort of destructive event, its properties do not match any known phenomenon. This means this source may be of a variety that scientists have never seen before.

The researchers do, however, have some ideas of what this source could be. Two of the three main possibilities to explain the X-ray source invoke gamma-ray burst (GRB) events, which are jetted explosions triggered either by the collapse of a massive star or by the merger of a neutron star with another neutron star or a black hole. If the jet is pointing towards the Earth, a burst of gamma-rays is detected. As the jet expands, it loses energy and produces weaker, more isotropic radiation at X-ray and other wavelengths.

Possible explanations for the CDF-S X-ray source, according to the researchers, are a GRB that is not pointed toward Earth, or a GRB that lies beyond the small galaxy. A third possibility is that a medium-sized black hole shredded a white dwarf star.

Thousands of hours of legacy data from the Hubble and Spitzer Space Telescopes helped determine that the event came from a faint, small galaxy about 10.7 billion light years from Earth. For a few minutes, the X-ray source produced a thousand times more energy than all the stars in this galaxy.

The mysterious X-ray source was not seen at any other time during the two and a half months of exposure time Chandra has observed the CDF-S region. Moreover, no similar events have yet been found in Chandra observations of other parts of the sky.

This X-ray source in the CDF-S has different properties from the as yet unexplained variable X-ray sources discovered in the elliptical galaxies NGC 5128 and NGC 4636 by Jimmy Irwin and collaborators. In particular, the CDF-S source is likely associated with the complete destruction of a neutron star or white dwarf, and is roughly 100,000 times more luminous in X-rays. It is also located in a much smaller and younger host galaxy, and is only detected during a single, several-hour burst.

Additional highly targeted searches through the Chandra archive and those of ESA's XMM-Newton and NASA's Swift satellite may uncover more examples of this type of variable object that have until now gone unnoticed. Future X-ray observations by Chandra and other X-ray telescopes may also reveal the same phenomenon from other objects.

Image Credit: X-ray: NASA/CXC/F.Bauer et al.
Explanation from: http://chandra.harvard.edu/photo/2017/cdfsxt1/

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Puyehue-Cordón Caulle Volcano Eruption

Osorno, Los Lagos, Chile

Image Credit: Ivan Alvarado

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Protoplanetary Disk HD 169142

This image depicts the dusty disc encircling the young, isolated star HD 169142. The Atacama Large Millimeter/submillimeter Array (ALMA) imaged this disc in high resolution by picking up faint signals from its constituent millimetre-sized dust grains. The vivid rings are thick bands of dust, separated by deep gaps.

Optimised to study the cold gas and dust of systems like HD 169142, ALMA’s sharp eyes have revealed the structure of many infant solar systems with similar cavities and gaps. A variety of theories have been proposed to explain them — such as turbulence caused by magnetorotational instability, or the fusing of dust grains — but the most plausible explanation is that these pronounced gaps were carved out by giant protoplanets.

When solar systems form gas and dust coalesce into planets. These planets then effectively spring clean their orbits, clearing them of gas and dust and herding the remaining material into well-defined bands. The deep gaps seen in this image are consistent with the presence of multiple protoplanets — a finding that agrees with other optical and infrared studies of the same system.

Observing such dusty protoplanetary discs with ALMA allows scientists to investigate the first steps of planet formation in a bid to unveil the evolutionary paths of these infant systems.

Image Credit: ALMA (ESO/NAOJ/NRAO)/ Fedele et al.
Explanation from: https://www.eso.org/public/images/potw1714a/

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