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Rahul kumar jaiswal
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Wondering why everyone is so sad about the end of NASA's Cassini mission. This picture should help clear things up. This stunning shot (isn't it so "film noir?") shows the Saturnian moons of Titan, Hyperion and Prometheus just beyond the planet's trademark rings. Cassini captured the image on July 14, 2014. More Cassini shots

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NASA's Cassini spacecraft has been snapping amazing photos of Saturn and its moons since 2004. See some of Cassini's latest spectacular photos of the Saturn system here. SHOWN HERE: This image of Saturn, taken by the Cassini probe on Feb. 26, 2016. The spacecraft captured this image from roughly 1.7 million miles, at 16 degrees above the ring plane using its wide-angle camera. The image reveals the planet’s odd hexagonal cloud pattern around the north pole

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This is where stardust comes from

Astronomers have spotted dust from some of the universe’s earliest supernovae, which are responsible for the elements in our Sun and solar system today.

The Atacama Large Millimeter/submillimeter Array (ALMA) in the Chilean Andes has made several groundbreaking discoveries since it was brought online in 2011. Able to image the sky in millimeter and submillimeter wavelengths, ALMA can spot emission associated with molecular gas and dust, which are cold and can be difficult or impossible to see at other wavelengths. Using this ability, ALMA has identified dust and gas in a galaxy that formed when our universe was only about 4 percent of its current age.

The galaxy is called A2744_YD4, and it’s the most distant galaxy ever found by ALMA. It sits at a redshift of 8.38, which is associated with a time when the universe was just 600 million years old.

Redshift measures the amount by which a distant object’s light is stretched by the expansion of the universe. Objects with a higher redshift are farther away, and thus we are looking at them as they appeared in the past. In the very nearby universe, objects have a redshift of nearly zero; high-redshift objects, such as A2744_YD4 with its redshift of 8.38, are extremely far away (the exact distance depends on the expansion history of the universe). It’s also important to note that redshift is not linear — redshifts of 0-1 are considered relatively nearby, while redshifts of 8-9 are some of the farthest objects we can currently see as we look back to the very early universe. The cosmic microwave background was produced at a redshift of about 1,000.

A2744_YD4’s cosmological “timestamp,” as given by its redshift, falls within the estimated age range for the Epoch of Reionization, which occurred somewhere around a redshift of 10, when the universe was about 400 million years old. The Epoch of Reionization is when the universe’s first luminous sources — stars, quasars, and galaxies — turned on and ionized neutral hydrogen atoms (that is, knocked their electrons away). Neutral hydrogen is opaque to short wavelengths of light, which means that it absorbs these wavelengths easily so the light cannot pass through. As neutral hydrogen throughout the universe was ionized, however, light could finally travel vast distances.

The detection of A2744_YD4 and its properties, which was made by an international team of astronomers led by Nicolas Laporte of University College London, is remarkable for several reasons.

A2744_YD4 is full of dust. In the press release accompanying the announcement, Laporte explained that “the detection of so much dust indicates early supernovae must have already polluted this galaxy.” Supernovae are the end result of massive stars, which blow away much of their interiors explosively as they die. Among the material blown away is dust, which is made up of elements such as aluminum, silicon, and carbon, and is spread across galaxies by these explosions. This dust is an integral component of today’s stars (like our Sun) and the planets surrounding them. In the very early universe, however, this dust was scarce, simply because the process of its creation and dispersion via supernovae hadn’t had much time to complete.

But in A2744_YD4, this process has apparently had enough time to progress. A2744_YD4 produces stars at a rate of 20 solar masses per year, which is a full 20 times the rate of our Milky Way’s comparatively paltry star formation rate of 1 solar mass per year. Based upon this rate, the group estimated that only about 200 million years were needed to form the dust seen in A2744_YD4.

Population III (Pop III) stars theoretically contain only hydrogen, helium, and very little if any “heavier” elements, such as lithium. This chemistry makes Pop III stars extremely metal-poor, if not devoid of metals altogether. (As a note, astronomers typically refer to any elements heavier than helium as “metals,” regardless of their classification on the periodic table.) Pop III stars probably began developing about 100 million years after the Big Bang. The metals created inside these massive stars began to spread via supernovae, and as the metal content of the universe increased, Pop II stars began to form about 13 billion years ago. Today, these stars are found in the bulges and haloes of galaxies, and while they’re still considered metal-poor, they contain metal abundances much greater than the very early universe.

The cycle of stellar birth and recycling continued, until about 10 billion years ago, Pop I stars began to form. Our Sun is a Pop I star, and the metals found inside it and our solar system can all be traced back to the same type of supernovae that spread dust (and metals) throughout A2744_YD4.

In addition to identifying the dust from these early supernovae, ALMA also spotted emission from ionized oxygen in A2744_YD4 as well. This is the earliest detection of ionized oxygen in the universe, breaking a previous record also held by ALMA (from a detection made in 2016).

All of this was made possible by the fact that A2744_YD4 sits behind a massive galaxy cluster called Abell 2744, also known as Pandora’s Cluster. The cluster is acting as a gravitational lens, magnifying the image from A2744_YD4 far behind it by about 1.8x and allowing astronomers to study this tiny, faraway galaxy.

These observations of A2744_YD4 and its contents are just an early step in tracing the origins of the universe’s earliest — and perhaps first, and most massive — stars, as well as exploring the epoch when stars and galaxies first began to shine. According to Laporte, “Further measurements of this kind offer the exciting prospect of tracing early star formation and the creation of the heavier chemical elements even further back into the early universe.”

About Images :

1. A2744_YD4 is so far away that it appears as a tiny smudge sitting behind the rich galaxy cluster Abell 2744. Shown in red are the ALMA observations that allowed Laporte and his team to identify dust throughout the galaxy.

Credits : ALMA (ESO/NAOJ/NRAO), NASA, ESA, ESO and D. Coe (STScI)/J. Merten (Heidelberg/Bologna)

2. ALMA observations have uncovered an extremely young, dusty galaxy already polluted with the products of supernovae, as pictured in this artist’s impression.

Credits : ESO/M. Kornmesser

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Saturn's Ravioli Moon

Saturn's moon Pan resembles a frozen ravioli in this new image from NASA's Cassini spacecraft. Pan is about the size of New York City and is the innermost known moon orbiting Saturn. Cassini flew within 15,268 miles (24,572 kilometers) of the strangely-shaped moon on Tuesday (March 7) and captured the closest images of the satellite to date. — Hanneke Weitering

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Credits : NASA/JPL-Caltech/Space Science Institute

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Hubble solves the mystery bulge at the center of the Milky Way

Our supermassive black hole has been on a diet for millions of years… but when did it last splurge

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The Milky Way appears as a relatively flat structure when viewed along its plane in visible light. Gamma-ray emission, however, paints a different picture: two huge structures billowing outward from the galaxy’s bulge like an enormous hourglass. Named the Fermi Bubbles, these structures are the result of the Milky Way’s supermassive black hole gorging itself on interstellar gas in the past. Using the Hubble Space Telescope (HST), astronomers have now determined just when these structured formed.

A team of astronomers led by Rongmon Bordoloi of the Massachusetts Institute of Technology has used distant quasars to trace the structure and motion of the northern Fermi Bubble, which rises 23,000 light-years above the plane of the Milky Way and contains enough cool gas to create 2 million Sun-size stars. By observing the ultraviolet light from 46 quasars with the Cosmic Origins Spectrograph (COS) on HST (and adding one quasar observation with HST’s Space Telescope Imaging Spectrograph), the team mapped out the motions of cool gas within the bubble to pin down its age: 6 to 9 million years.

Most galaxies contain a supermassive black hole at the center, and our Milky Way is no exception. Sgr A* resides in the Milky Way’s bulge and has a mass equivalent to 4.5 million solar masses. Today, Sgr A* is relatively quiet, accreting slowly as the galaxy ages. By contrast, quasars are young, massive supermassive black holes at the centers of galaxies in the early universe, sucking down huge amounts of gas and dust that shine brightly as the material is funneled into an accretion disk before finally passing into the black hole. Like these younger black holes, astronomers believe that our own supermassive black hole was once more active, at a time when the galaxy was still forming and material was more plentiful for accretion.

Sometimes, though, material doesn’t actually make it all the way into the black hole. Matter can escape along the black hole’s spin axis, exiting the area — and often the galaxy altogether — as huge outflows that span tens or hundreds of thousands of light-years. The Milky Way’s Fermi Bubbles are such an outflow; they were discovered in 2015 and named after NASA’s Fermi Gamma-Ray Telescope, which spotted them.

Learning more about the origins of these outflows requires information about their motion. “We have traced the outflows of other galaxies, but we have never been able to actually map the motion of the gas,” said Bordoloi in a press release announcing his group’s results. The work also appeared in the January 10, 2017 edition of The Astrophysical Journal. “The only reason we could do it here is because we are inside the Milky Way. This vantage point gives us a front-row seat to map out the kinematic structure of the Milky Way outflow.”

As the quasars’ light travels through the bubble to reach Earth, it highlights the gas in bubble itself, allowing astronomers to determine information such as its chemical composition, temperature, and motion. The “cool” gas in the northern Fermi Bubble, which contains elements such as silicon and carbon, was clocked at 2 million miles per hour (3 million kph) an reaches temperatures of 17,700 degrees Fahrenheit (9,800 degrees Celsius).

Such cool gas is actually likely gas from the disk of the galaxy that has been swept up by and integrated into the outflow itself, which has temperatures of up to 18 million degrees F (nearly 10 million degrees C). It is these high temperatures that cause the gas to shine in energetic light, such as gamma rays.

Once the gas’ motion — its direction of movement and velocity — was measured, astronomers used this data to turn back the clock and pinpoint when the gas started moving. This origin is also the last known “big meal” enjoyed by Sgr A*, which hasn’t managed to suck down such a significant amount of matter ever since.

“What we find is that a very strong, energetic event happened 6 million to 9 million years ago,” Bordoloi explained. “It may have been a cloud of gas flowing into the black hole, which fired off jets of matter, forming the twin lobes of hot gas seen in X-ray and gamma-ray observations. Ever since then, the black hole has just been eating snacks.”

About Image : The Fermi Bubbles are two huge structures “burped out” by the Milky Way’s supermassive black hole and visible in X-ray and gamma-ray light.

Credits : NASA's Goddard Space Flight Center


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Multiwavelength View of Supernova 1987A

Astronomers combined observations from three different observatories to produce this colorful, multi-wavelength image of the intricate remains of Supernova 1987A.

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The red color shows newly formed dust in the center of the supernova remnant, taken at submillimeter wavelengths by the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile.

The green and blue hues reveal where the expanding shock wave from the exploded star is colliding with a ring of material around the supernova. The green represents the glow of visible light, captured by NASA’s Hubble Space Telescope. The blue color reveals the hottest gas and is based on data from NASA’s Chandra X-ray Observatory.

The ring was initially made to glow by the flash of light from the original explosion. Over subsequent years the ring material has brightened considerably as the explosion’s shock wave slams in it.

Supernova 1987A resides 163,000 light-years away in the Large Magellanic Cloud, where a firestorm of star birth is taking place.

The ALMA, Hubble, and Chandra images at the bottom of the graphic were used to make up the multiwavelength view.

Credits :

Image credit: NASA, ESA, and A. Angelich (NRAO/AUI/NSF)
Hubble credit: NASA, ESA, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation)
Chandra credit: NASA/CXC/Penn State/K. Frank et al.
ALMA credit: ALMA (ESO/NAOJ/NRAO) and R. Indebetouw (NRAO/AUI/NSF)

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Partial Eclipse Taken by Proba-2's SWAP imager

About Image :
The European Space Agency's Proba-2 satellite captured a partial solar eclipse from space on Feb. 26. Meanwhile, observers in Earth's southern hemisphere enjoyed an annular solar eclipse, in which the moon blocked the sun and created a "ring of fire" in the sky. From Proba-2's point of view, the moon crossed the sun off-center and appeared to take a bite out of its shining face. This image was taken by Proba-2's SWAP imager, which observes the sun in ultraviolet light to capture its turbulent surface and its swirling corona. — Hanneke Weitering

Credit : ESA/Royal Observatory of Belgium

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Weird Asteroid Split in Half and Grew Glowing Dust Tails

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A recently discovered "asteroid pair" is the youngest such duo known in Earth's solar system, and it appears to have sprouted twin comet-like tails, new observations reveal.

This asteroid pair, known as P/2016 J1, was discovered in 2016. Asteroid pairs are not uncommon in the solar system's main asteroid belt. These duos typically form when a parent asteroid breaks in two pieces following a collision with a foreign body, or when the rocky body experiences an excess rotational speed or destabilization of its initial orbit, scientists have said.

The new observations of were made by researchers using the Great Telescope of the Canary Islands (GTC) and the Canada-France-Hawaii Telescope (CFHT) on Hawaii's Mauna Kea volcano. The team found "that the asteroid fragmented approximately six years ago, which makes it the youngest known asteroid pair in the solar system to date," project leader Fernando Moreno, a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) in Spain, said in a statement.

When studying P/2016 J1, astronomers discovered that the asteroid pair was activated between the end of 2015 and the beginning of 2016, when the space rocks reached perihelion — the point in their orbit when they are closest to the sun. They remained that way for roughly six to nine months. Their activation is a separate event from that which caused the asteroid to break in half, according to the statement.

Although the two members of the asteroid pair are not gravitationally linked, the rocky bodies have similar orbits around the sun, the researchers said. P/2016 J1 travels in a quasi-circular orbit between Mars and Jupiter, and therefore doesn't get close enough to the sun to experience the temperature changes that create the dust tails observed on comets, the scientists said.

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Instead, the new observations suggest that "the dust emission is due to the sublimation [shift from solid to gaseous phase] of ice that was left exposed after the fragmentation," Moreno said in the statement from the IAA-CSIC.

About Image :

1. Hubble Space Telescope view showing the dust tail of the "activated asteroid" P/2013 P5. Astronomers have recently spotted tails coming from the youngest-known fragmented asteroid pair in the solar system, a duo known as P/2016 J1.

Credit: NASA/ESA

2. These observations of the two asteroid fragments that make up P/2016 J1 (called J1-A and J1-B) from May 15, 2016 show the central regions of the space rocks, as well as the diffuse blots of their dust tails.

Credit: IAA-CSIC

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This tiny solar system packs in seven Earth-size planets

TRAPPIST-1 has a solar system like no other. The tiny, tiny red dwarf is just barely big enough to be considered a star and is, radius-wise, a hair bigger than Jupiter. When it was announced last May there was some excitement: the system had three Earth-sized planets and they might all be habitable.

We’re going to have to revise that, though. It has seven planets. The results of an intensive study were published today in Nature.

TRAPPIST-1 is so small that it resembles Jupiter and its planets appear more like the jovian moons when laid out distance-wise. TRAPPIST-1b has an orbital period of just 1.5 days and orbits at 1 percent the distance between the Sun and the Earth. Because TRAPPIST-1 is so small, though, instead of dooming the planet it could give it just a slightly balmier-than-comfortable temperature.

The May 2016 events that led to the initial discovery of the planets actually ended up being somewhat in error. Planets TRAPPIST-1b and TRAPPIST-1c were easily confirmed, but TRAPPIST-1d was not. TRAPPIST-1d had a bizarre, hard to constrain orbit much longer than the other planets, and was believed to potentially have an eccentric orbit.

But there was no TRAPPIST-1d. Or at least not as it appeared. Two transits were witnessed during the first observing campaign, both believed to be the outermost of the three worlds. But those two transits were actually two distinct events.

“The first transit and the second transit were coming from different planets,” Michaël Gillon, a professor at the University of Leige and lead author of the paper, said. “In fact, the second transit was two planets passing at the same time.”

Like no other

That brings us to five planets. Intensive studies using both the TRAPPIST telescope and NASA’s Spitzer telescope helped refine the orbit of the planets and drew out the presence of two more from the data. TRAPPIST-1b, -1c, -1f, and -1g are all very slightly larger than Earth. -1e is slightly smaller than Earth. -1d and -1h are closer to Mars in size.

While the exact masses and orbital periods aren’t known yet, preliminary results suggest that they may be in resonance. That means that when -1b orbits eight times, -1c completes five orbits, often marked as 8:5. -1c and -1d are in 5:3 resonance; -1d and -1e are in 3:2, as are -1e and -1f. -1f and -1g are in 4:3.

All of them seem to be in the habitable zone of TRAPPIST-1. That means that they could, under the right conditions, sustain surface water, but there’s no proof that any of the planets do. For instance, in our solar system Venus and Mars are in the habitable zone, but both are fairly inhospitable in our present time.

Of the seven, the researchers believe that -1e, -1f, and -1g are the likeliest to be habitable based on where they sit in the solar system.

While seven planets have been confirmed, that’s not all the system may hold in store.

“It is just the beginning for many reasons — there might be more on top of that,” Julien de Wit, a co-author on the paper, says.

Slow your roll

There are other considerations before we declare the planets quite ripe for life, though. M-dwarf stars like TRAPPIST-1 tend to start out very active with high energy flare events. This could strip away the atmosphere of young planets.

At this point, according to co-author Emmanuël Jehin, most comets would have been cleared out of the system and thus unable to replenish the atmospheres. But other forces like volcanism could work to stabilize the atmospheres, strengthening them against the relentless flare events.

M-dwarfs finally settle down after the first 3 billion years or so, though many stellar events still occur. For instance, Proxima Centauri is an active flare star, which could doom its habitable zone planet, Proxima Centauri b, from ever forming complex life. But TRAPPIST-1 is cooler and less active than Proxima.

“If you compare it Proxima Centauri, it’s much less, but if you compare it to the Sun, it’s much more,” Gillon said.

TRAPPIST-1 and its seven (!!!) planets are high on the list of planets to be observed by the James Webb Space Telescope (JWST) after it launches next year. A follow-up telescope to TRAPPIST, SPECULOOS, will be able to find more TRAPPIST-type objects. TRAPPIST itself only looked at 50 ultracool stars for planets, while SPECULOOS will look at tens of thousands.

JWST will monitor transits of worlds in the TRAPPIST stars, hoping to capture a glimmer of their atmospheres. If they seem to be thin and water-dominated, we may indeed be looking at a quite Earth-like planet. Or even three of them. Maybe, just maybe, seven.

“We have seven targets that we can study in great depth, and they can give us a completely new insight into planet formation and stellar history,” de Wit says.

TRAPPIST-1 system

Credit: NASA/JPL-Caltech and Roen Kelly
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A supermassive black hole spent more than a decade consuming a star

Hungry Black Hole

A supermassive black hole has been tearing apart and eating a star for so long it set a new record.

According to researchers, this tidal disruption event was 10 times longer than any other star’s death, which either means the black hole was destroying an incredibly large star or it thoroughly torn apart a smaller star.

The team of researchers began observing the TDE that destroyed the too close star in July 2005, using NASA’s Chandra X-ray Observatory and Swift satellite and ESA’s WMM-Newton.

This black hole, known as XJ1500+0154, is at the center of a host galaxy about 1.8 billion light-years from Earth. It reached peak brightness in June 2008, and has been on researchers’ radars ever since.

“For most of the time we’ve been looking at this object, it has been growing rapidly,” James Guillochon of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. and co-author of the study said. “This tells us something unusual — like a star twice as heavy as our Sun — is being fed into the black hole.”

Finding this drawn out death of a star by black hole shows not only that supermassive black holes can grow, but it also gives researchers more information about advanced black holes and how they came to be.

According to the researchers, the star that the black hole is feeding on will diminish in the next several years, and will therefore cause the brightness of XJ1500+0154 to fade as well.

Black Hole Meal Sets Record for Length and Size

Image and Credit : X-ray: NASA/CXC/UNH/D.Lin et al, Optical: CFHT, Illustration: NASA/CXC/M.Weiss

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