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Anand Sankar
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There is nothing noble in being superior to your fellow men. True nobility lies in being superior to your former self.
There is nothing noble in being superior to your fellow men. True nobility lies in being superior to your former self.

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Chino y Nacho - Andas En Mi Cabeza ft. Daddy Yankee
Volume: ▁ ▂ ▃ ▄ ▅ ▆ █ 100 %¸.•*¨*•♫
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Rings Around the Ring Nebula

Image Credit: Hubble, Large Binocular Telescope, Subaru Telescope; Composition & Copyright: Robert Gendler

Explanation: There is much more to the familiar Ring Nebula (M57), however, than can be seen through a small telescope. The easily visible central ring is about one light-year across, but this remarkably deep exposure - a collaborative effort combining data from three different large telescopes - explores the looping filaments of glowing gas extending much farther from the nebula's central star. This remarkable composite image includes narrowband hydrogen image, visible light emission, and infrared light emission. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from a dying, sun-like star. The Ring Nebula is about 2,000 light-years away toward the musical constellation Lyra.



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Hubble and Gaia Team Up to Fuel Cosmic Conundrum

Using the power and synergy of two space telescopes, astronomers have made the most precise measurement to date of the universe’s expansion rate.

The results further fuel the mismatch between measurements for the expansion rate of the nearby universe, and those of the distant, primeval universe — before stars and galaxies even existed.

This so-called “tension” implies that there could be new physics underlying the foundations of the universe. Possibilities include the interaction strength of dark matter, dark energy being even more exotic than previously thought, or an unknown new particle in the tapestry of space.

Combining observations from NASA’s Hubble Space Telescope and the European Space Agency’s (ESA) Gaia space observatory, astronomers further refined the previous value for the Hubble constant, the rate at which the universe is expanding from the big bang 13.8 billion years ago.

But as the measurements have become more precise, the team’s determination of the Hubble constant has become more and more at odds with the measurements from another space observatory, ESA’s Planck mission, which is coming up with a different predicted value for the Hubble constant.

Planck mapped the primeval universe as it appeared only 360,000 years after the big bang. The entire sky is imprinted with the signature of the big bang encoded in microwaves. Planck measured the sizes of the ripples in this Cosmic Microwave Background (CMB) that were produced by slight irregularities in the big bang fireball. The fine details of these ripples encode how much dark matter and normal matter there is, the trajectory of the universe at that time, and other cosmological parameters.

These measurements, still being assessed, allow scientists to predict how the early universe would likely have evolved into the expansion rate we can measure today. However, those predictions don’t seem to match the new measurements of our nearby contemporary universe.

“With the addition of this new Gaia and Hubble Space Telescope data, we now have a serious tension with the Cosmic Microwave Background data,” said Planck team member and lead analyst George Efstathiou of the Kavli Institute for Cosmology in Cambridge, England, who was not involved with the new work.

“The tension seems to have grown into a full-blown incompatibility between our views of the early and late time universe,” said team leader and Nobel Laureate Adam Riess of the Space Telescope Science Institute and the Johns Hopkins University in Baltimore, Maryland. “At this point, clearly it’s not simply some gross error in any one measurement. It’s as though you predicted how tall a child would become from a growth chart and then found the adult he or she became greatly exceeded the prediction. We are very perplexed.”

In 2005, Riess and members of the SHOES (Supernova H0 for the Equation of State) team set out to measure the universe’s expansion rate with unprecedented accuracy. In the following years, by refining their techniques, this team shaved down the rate measurement’s uncertainty to unprecedented levels. Now, with the power of Hubble and Gaia combined, they have reduced that uncertainty to just 2.2 percent.

Because the Hubble constant is needed to estimate the age of the universe, the long-sought answer is one of the most important numbers in cosmology. It is named after astronomer Edwin Hubble, who nearly a century ago discovered that the universe was uniformly expanding in all directions—a finding that gave birth to modern cosmology.

Galaxies appear to recede from Earth proportional to their distances, meaning that the farther away they are, the faster they appear to be moving away. This is a consequence of expanding space, and not a value of true space velocity. By measuring the value of the Hubble constant over time, astronomers can construct a picture of our cosmic evolution, infer the make-up of the universe, and uncover clues concerning its ultimate fate.

The two major methods of measuring this number give incompatible results. One method is direct, building a cosmic “distance ladder” from measurements of stars in our local universe. The other method uses the CMB to measure the trajectory of the universe shortly after the big bang and then uses physics to describe the universe and extrapolate to the present expansion rate. Together, the measurements should provide an end-to-end test of our basic understanding of the so-called “Standard Model” of the universe. However, the pieces don’t fit.

Using Hubble and newly released data from Gaia, Riess’ team measured the present rate of expansion to be 73.5 kilometers (45.6 miles) per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it appears to be moving 73.5 kilometers per second faster. However, the Planck results predict the universe should be expanding today at only 67.0 kilometers (41.6 miles) per second per megaparsec. As the teams’ measurements have become more and more precise, the chasm between them has continued to widen, and is now about four times the size of their combined uncertainty.

Over the years, Riess’ team has refined the Hubble constant value by streamlining and strengthening the “cosmic distance ladder,” used to measure precise distances to nearby and far-off galaxies. They compared those distances with the expansion of space, measured by the stretching of light from nearby galaxies. Using the apparent outward velocity at each distance, they then calculated the Hubble constant.

To gauge the distances between nearby galaxies, his team used a special type of star as cosmic yardsticks or milepost markers. These pulsating stars, called Cephied variables, brighten and dim at rates that correspond to their intrinsic brightness. By comparing their intrinsic brightness with their apparent brightness as seen from Earth, scientists can calculate their distances.

Gaia further refined this yardstick by geometrically measuring the distance to 50 Cepheid variables in the Milky Way. These measurements were combined with precise measurements of their brightnesses from Hubble. This allowed the astronomers to more accurately calibrate the Cepheids and then use those seen outside the Milky Way as milepost markers.

“When you use Cepheids, you need both distance and brightness,” explained Riess. Hubble provided the information on brightness, and Gaia provided the parallax information needed to accurately determine the distances. Parallax is the apparent change in an object’s position due to a shift in the observer’s point of view. Ancient Greeks first used this technique to measure the distance from Earth to the Moon.

“Hubble is really amazing as a general-purpose observatory, but Gaia is the new gold standard for calibrating distance. It is purpose-built for measuring parallax—this is what it was designed to do,” Stefano Casertano of the Space Telescope Science Institute and a member of the SHOES team added. “Gaia brings a new ability to recalibrate all past distance measures, and it seems to confirm our previous work. We get the same answer for the Hubble constant if we replace all previous calibrations of the distance ladder with just the Gaia parallaxes. It’s a crosscheck between two very powerful and precise observatories.”

The goal of Riess’ team is to work with Gaia to cross the threshold of refining the Hubble constant to a value of only one percent by the early 2020s. Meanwhile, astrophysicists will likely continue to grapple with revisiting their ideas about the physics of the early universe.

The Riess team's latest results are published in the July 12 issue of the Astrophysical Journal.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

The Image

Using two of the world’s most powerful space telescopes — NASA’s Hubble and ESA’s Gaia — astronomers have made the most precise measurements to date of the universe’s expansion rate. This is calculated by gauging the distances between nearby galaxies using special types of stars called Cepheid variables as cosmic yardsticks. By comparing their intrinsic brightness as measured by Hubble, with their apparent brightness as seen from Earth, scientists can calculate their distances. Gaia further refines this yardstick by geometrically measuring the distances to Cepheid variables within our Milky Way galaxy. This allowed astronomers to more precisely calibrate the distances to Cepheids that are seen in outside galaxies.


Credits: NASA, ESA, and A. Feild (STScI)
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Messier 24: Sagittarius Star Cloud

Image Credit & Copyright: Roberto Colombari
Explanation: Unlike most entries in Charles Messier's famous catalog of deep sky objects, M24 is not a bright galaxy, star cluster, or nebula. It's a gap in nearby, obscuring interstellar dust clouds that allows a view of the distant stars in the Sagittarius spiral arm of our Milky Way galaxy. When you gaze at the star cloud with binoculars or small telescope you are looking through a window over 300 light-years wide at stars some 10,000 light-years or more from Earth. Sometimes called the Small Sagittarius Star Cloud, M24's luminous stars fill the left side of this gorgeous starscape. Covering about 4 degrees or the width of 8 full moons in the constellation Sagittarius, the telescopic field of view contains many small, dense clouds of dust and nebulae toward the center of the Milky Way, including reddish emission from IC 1284 near the top of the frame.
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From the Galactic Plane through Antares

Image Credit & License: Rogelio Bernal Andreo (Deep Sky Colors)

Explanation: Behold one of the most photogenic regions of the night sky, captured impressively. Featured, the band of our Milky Way Galaxy runs diagonally along the far left, while the colorful Rho Ophiuchus region including the bright orange star Antares is visible just right of center, and the nebula Sharpless 1 (Sh2-1) appears on the far right. Visible in front of the Milk Way band are several famous nebulas including the Eagle Nebula (M16), the Trifid Nebula (M20), and the Lagoon Nebula (M8). Other notable nebulas include the Pipe and Blue Horsehead. In general, red emanates from nebulas glowing in the light of exited hydrogen gas, while blue marks interstellar dust preferentially reflecting the light of bright young stars. Thick dust appears otherwise dark brown. Large balls of stars visible include the globular clusters M4, M9, M19, M28, and M80, each marked on the annotated companion image. This extremely wide field -- about 50 degrees across -- spans the constellations of Sagittarius is on the lower left, Serpens on the upper left, Ophiuchus across the middle, and Scorpius on the right. It took over 100 hours of sky imaging, combined with meticulous planning and digital processing, to create this image.

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Northern Lights and Noctilucent Clouds
Image Credit & Copyright: Adrien Mauduit

Explanation: Skies after the near-solstice sunset on June 17 are reflected in this calm lake. The tranquil twilight scene was captured near Bashaw, Alberta, Canada, northern planet Earth. Usually spotted at high latitudes in summer months, night shining or noctilucent clouds hang just above the horizon, transfusing light into a darker sky. Near the edge of space, the icy apparitions are condensations on meteoric dust or volcanic ash still in sunlight at extreme altitudes. Also near the edge of space on this short northern night, solar activity triggered the lovely apparition of aurora borealis or northern lights.
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Jupiter Season, Hawaiian Sky
Image Credit & Copyright: Tunç Tezel (TWAN)

Explanation: Volcanic activity on the Big Island of Hawaii has increased since this Hawaiian night skyscape was recorded earlier this year. Recent vents and lava flows are about 30 kilometers to the east, the direction of the blowing smoke and steam in the panoramic view of the Kilauea caldera with Halemaumau crater taken from Volcanoes National Park. Still, this year Jupiter is bright in late spring to early summer skies. High in the south it is easily the brightest celestial beacon in the scene where the central bulge of the Milky Way seems to rise above vapors and clouds. Yellowish Antares is the bright star near the end of the dark rivers of dust seen toward the center of our galaxy. Near the horizon, stars Alpha and Beta Centauri and the compact Southern Cross shine through the almost too bright volcanic smoke.
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The Clash of NGC 3256

Image Credit & License: NASA, ESA, Hubble Space Telescope

Explanation: Marked by an unusually bright central region, swirling dust lanes, and far flung tidal tails, peculiar NGC 3256 is the aftermath of a truly cosmic collision. The 500 million year old clash of two separate galaxies spans some 100 thousand light-years in this sharp Hubble view. Of course when two galaxies collide, individual stars rarely do. Giant galactic clouds of molecular gas and dust do interact though, and produce spectacular bursts of star formation. In this galaxy clash, the two original spiral galaxies had similar masses. Their disks are no longer distinct and the two galactic nuclei are hidden by obscuring dust. On the timescale of a few hundred million years the nuclei will likely also merge as NGC 3256 becomes a single large elliptical galaxy. NGC 3256 itself is nearly 100 million light-years distant toward the southern sailing constellation Vela. The frame includes many even more distant background galaxies and spiky foreground stars.
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Six Planets from Yosemite

Image Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)

Explanation: The five naked-eye planets, Mercury, Venus, Mars, Jupiter and Saturn, have been seen since ancient times to wander the night skies of planet Earth. So it could be remarkable that on this night, standing at the side of a clear, calm lake, six planets can be seen with the unaided eye. Have a look. Very bright and easy to spot for skygazers, yellowish Mars is left of a pale Milky Way. Saturn is immersed in the glow of the Milky Way's diffuse starlight. Jupiter is very near the horizon on the right, shining beyond the trees against the glow of distant city lights. Last weekend, while admiring this night time view across beautiful, high-altitude Lake Tanaya in Yosemite National Park, a thoughtful and reflective observer could probably see three planets more.
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As Solar Wind Blows, Our Heliosphere Balloons
Part 1 of 2

What happens when the solar wind suddenly starts to blow significantly harder? According to two recent studies, the boundaries of our entire solar system balloon outward — and an analysis of particles rebounding off of its edges will reveal its new shape.

In late 2014, NASA spacecraft detected a substantial change in the solar wind. For the first time in nearly a decade, the solar wind pressure — a combined measure of its speed and density — had increased by approximately 50 percent and remained that way for several years thereafter. Two years later, the Interstellar Boundary Explorer, or IBEX, spacecraft detected the first sign of the aftermath. Solar wind particles from the 2014 pressure increase had reached the edge of the heliosphere, neutralized themselves, and shot all the way back to Earth. And they had a story to tell.

In two recent articles, scientists used IBEX data along with sophisticated numerical models to understand what these rebounding atoms can tell us about the evolving shape and structure of our heliosphere, the giant bubble carved out by the solar wind.

“The results show that the 2014 solar wind pressure increase has already propagated from the Sun to the outer heliosphere, morphing and expanding our heliosphere’s boundaries in their closest direction,” said David McComas, the principal investigator for the IBEX mission at Princeton University in Princeton, New Jersey. “IBEX data pouring in over the next few years will let us chart the expansion and evolving structure of the other portions of the heliosphere’s outer boundaries.”

From the Sun to the edge of the solar system — and back

At the crux of the story are energetic neutral atoms – high-energy particles produced at the very edge of our solar system.

As the solar wind flows out from the Sun at supersonic speeds, it blows up a bubble known as the heliosphere. The heliosphere encases all the planets in our solar system and much of the space beyond them, separating the domain of our Sun from that of interstellar space.

But the solar wind’s journey from the Sun is not a smooth ride. On its way to the very edge of our heliosphere, known as the heliopause, the solar wind passes through distinct layers. The first of these is known as the termination shock.

Before passing the termination shock, the solar wind expands rapidly, largely unimpeded by outside material.

“But at the termination shock, roughly 9.3 billion miles away from us in every direction, the solar wind slows down abruptly. Beyond this point it continues to move outwards, but it is much hotter,” said Eric Zirnstein, lead author of one of the papers at Princeton.

Once beyond the termination shock, solar wind particles enter a special limbo zone known as the heliosheath. While the termination shock is essentially spherical, the edges of the heliosphere are thought to describe more of an arc around the Sun as it moves through space — closer to the Sun toward the front, and extending long behind it, not unlike a comet with a tail. Along these boundaries, solar wind particles mix with particles from interstellar space. Collisions are inevitable: the hot, electrically-charged solar wind particles bang into the slower, colder neutral atoms from interstellar space, stealing an electron and becoming neutral themselves.

“From there they go travelling ballistically through space, and some make it all the way back to Earth,” Zirnstein said. “These are the energetic neutral atoms that IBEX observes.”

In late 2016, when IBEX’s energetic neutral atom imager began to pick up an unusually strong signal, Professor McComas and his team set out to investigate its cause. Their findings are reported in an article published on March 20, 2018, in the Astrophysical Journal Letters.

The energetic neutral atoms were coming from about 30 degrees south of the interstellar upwind direction, where the heliosheath was known to be closest to Earth.

To quantify its connection to the 2014 solar wind pressure increase, McComas and his team turned to numerical simulations, working out how such a pressure increase could affect the energetic neutral atoms that IBEX observes.

“These types of simulations involve a model for the physics, which then gets turned into equations, which are in turn solved on a supercomputer,” said Jacob Heerikhuisen, a coauthor on both papers at the University of Alabama in Huntsville.

Using computer models, the team simulated an entire heliosphere, jolted it with a solar wind pressure increase, and let it run the numbers. The simulation completed a story only hinted at by the data.

According to the simulation, once the solar wind hits the termination shock it creates a pressure wave. That pressure wave continues on to the edge of the heliosphere and partially rebounds backwards, forcing particles to collide within the (now much denser) heliosheath environment that it just passed through. That’s where the energetic neutral atoms that IBEX observed were born.

The simulations provided a compelling case: IBEX was indeed observing the results of the 2014 solar wind pressure increase, more than two years later.

But the simulation didn’t stop there. It also revealed that the 2014 solar wind pressure increase would, over time, continue to blow up the heliosphere even further. Three years after the solar wind pressure increase — by the time the article was published — the termination shock, the inner bubble within the heliosphere, should expand by seven astronomical units, or seven times the distance from Earth to the Sun. The heliopause, the outer bubble, should expand by two astronomical units, with an additional two the following year.

In short, by cranking up the pressure of the solar wind, our heliosphere today is bigger than it was just a few years ago.

The Image

An illustration depicting the layers of the heliosphere.

Credits: NASA/IBEX/Adler Planetarium

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