Many celestial objects are beautiful – swirling spiral galaxies or glittering clusters of stars are notable examples. But some of the most striking scenes are created during the death throes of intermediate-mass stars, when great clouds of superheated gas are expelled into space. These dying breaths form planetary nebulas like NGC 6302, captured here in this image from the NASA/ESA Hubble Space Telescope. Continue reading Butterfly death throes
A team of astronomers using NASA’s Hubble Space Telescope has taken an important step closer to finding the birth certificate of a star that’s been around for a very long time.
“We have found that this is the oldest known star with a well-determined age,” said Howard Bond of Pennsylvania State University in University Park, Pa., and the Space Telescope Science Institute in Baltimore, Md.
The star could be as old as 14.5 billion years (plus or minus 0.8 billion years), which at first glance would make it older than the universe’s calculated age of about 13.8 billion years, an obvious dilemma.
But earlier estimates from observations dating back to 2000 placed the star as old as 16 billion years. And this age range presented a potential dilemma for cosmologists. “Maybe the cosmology is wrong, stellar physics is wrong, or the star’s distance is wrong,” Bond said. “So we set out to refine the distance.”
The new Hubble age estimates reduce the range of measurement uncertainty, so that the star’s age overlaps with the universe’s age — as independently determined by the rate of expansion of space, an analysis of the microwave background from the big bang, and measurements of radioactive decay.
This “Methuselah star,” cataloged as HD 140283, has been known about for more than a century because of its fast motion across the sky. The high rate of motion is evidence that the star is simply a visitor to our stellar neighborhood. Its orbit carries it down through the plane of our galaxy from the ancient halo of stars that encircle the Milky Way, and will eventually slingshot back to the galactic halo.
This conclusion was bolstered by the 1950s astronomers who were able to measure a deficiency of heavier elements in the star as compared to other stars in our galactic neighborhood. The halo stars are among the first inhabitants of our galaxy and collectively represent an older population from the stars, like our sun, that formed later in the disk. This means that the star formed at a very early time before the universe was largely “polluted” with heavier elements forged inside stars through nucleosynthesis. (The Methuselah star has an anemic 1/250th as much of the heavy element content of our sun and other stars in our solar neighborhood.)
The star, which is at the very first stages of expanding into a red giant, can be seen with binoculars as a 7th-magnitude object in the constellation Libra.
Hubble’s observational prowess was used to refine the distance to the star, which comes out to be 190.1 light-years. Bond and his team performed this measurement by using trigonometric parallax, where an apparent shift in the position of a star is caused by a change in the observer’s position. The results are published in the February 13 issue of the Astrophysical Journal Letters.
The parallax of nearby stars can be measured by observing them from opposite points in Earth’s orbit around the sun. The star’s true distance from Earth can then be precisely calculated through straightforward triangulation.
Once the true distance is known, an exact value for the star’s intrinsic brightness can be calculated. Knowing a star’s intrinsic brightness is a fundamental prerequisite to estimating its age.
Before the Hubble observation, the European Space Agency’s Hipparcos satellite made a precise measurement of the star’s parallax, but with an age measurement uncertainty of 2 billion years. One of Hubble’s three Fine Guidance Sensors measured the position of the Methuselah star. It turns out that the star’s parallax came out to be virtually identical to the Hipparcos measurements. But Hubble’s precision is five times better that than of Hipparcos. Bond’s team managed to shrink the uncertainty so that the age estimate was five times more precise.
With a better handle on the star’s brightness Bond’s team refined the star’s age by applying contemporary theories about the star’s burn rate, chemical abundances, and internal structure. New ideas are that leftover helium diffuses deeper into the core and so the star has less hydrogen to burn via nuclear fusion. This means it uses fuel faster and that correspondingly lowers the age.
Also, the star has a higher than predicted oxygen-to-iron ratio, and this too lowers the age. Bond thinks that further oxygen measurement could reduce the star’s age even more, because the star would have formed at a slightly later time when the universe was richer in oxygen abundance. Lowering the upper age limit would make the star unequivocally younger than the universe.
“Put all of those ingredients together and you get an age of 14.5 billion years, with a residual uncertainty that makes the star’s age compatible with the age of the universe,” said Bond. “This is the best star in the sky to do precision age calculations by virtue of its closeness and brightness.”
This Methuselah star has seen many changes over its long life. It was likely born in a primeval dwarf galaxy. The dwarf galaxy eventually was gravitationally shredded and sucked in by the emerging Milky Way over 12 billion years ago.
The star retains its elongated orbit from that cannibalism event. Therefore, it’s just passing through the solar neighborhood at a rocket-like speed of 800,000 miles per hour. It takes just 1,500 years to traverse a piece of sky with the angular width of the full Moon. The star’s proper motion angular rate is so fast (0.13 milliarcseconds an hour) that Hubble could actually photograph its movement in literally a few hours….
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This thin, glittering streak of stars is the spiral galaxy ESO 121-6, which lies in the southern constellation of Pictor (The Painter’s Easel). Viewed almost exactly side-on, the intricate structure of the swirling arms is hidden, but the full length of the galaxy can be seen — including the intense glow from the central bulge, a dense region of tightly packed young stars sitting at the center of the spiral arms.
Tendrils of dark dust can be seen across the frame, partially obscuring the bright center of the galaxy and continuing out towards the smattering of stars at its edges, where the dust lanes and shapes melt into the inky background. Numerous nearby stars and galaxies are visible as small smudges in the surrounding sky, and the brightest stars are dazzlingly prominent towards the bottom left of the image.
ESO 121-6 is a galaxy with patchy, loosely-wound arms and a relatively faint central bulge. It actually belongs to a group of galaxies, a clump of no more than 50 similar structures all loosely bound to one another by gravity. The Milky Way is also a member of a galactic group, known as the Local Group.
Read more: http://www.nasa.gov/mission_pages/hubble/science/eso121-6.html
This the season for holiday decorating and tree-trimming. Not to be left out, astronomers using NASA’s Hubble Space Telescope have photographed a festive-looking nearby planetary nebula called NGC 5189. The intricate structure of this bright gaseous nebula resembles a glass-blown holiday ornament with a glowing ribbon entwined.
Planetary nebulae represent the final brief stage in the life of a medium-sized star like our sun. While consuming the last of the fuel in its core, the dying star expels a large portion of its outer envelope. This material then becomes heated by the radiation from the stellar remnant and radiates, producing glowing clouds of gas that can show complex structures, as the ejection of mass from the star is uneven in both time and direction.
This is a video zoom into the region of sky containing the planetary nebula NGC 5189. The nebula has a knotty and filamentary structure surrounding bluish lobes. The nebula was formed by gases escaping from a dying Sun-like star. The nebula is located several thousand light-years away in the southern constellation Musca. Credit: NASA, ESA, and G. Bacon (STScI)
A spectacular example of this beautiful complexity is seen in the bluish lobes of NGC 5189. Most of the nebula is knotty and filamentary in its structure. As a result of the mass-loss process, the planetary nebula has been created with two nested structures, tilted with respect to each other, that expand away from the center in different directions.
This double bipolar or quadrupolar structure could be explained by the presence of a binary companion orbiting the central star and influencing the pattern of mass ejection during its nebula-producing death throes. The remnant of the central star, having lost much of its mass, now lives its final days as a white dwarf. However, there is no visual candidate for the possible companion.
The bright golden ring that twists and tilts through the image is made up of a large collection of radial filaments and cometary knots. These are usually formed by the combined action of photo-ionizing radiation and stellar winds.
This image was taken with Hubble’s Wide Field Camera 3 on October 8, 2012, in filters tuned to the specific colors of fluorescing sulfur, hydrogen, and oxygen atoms. Broad filters in the visible and near-infrared were used to capture the star colors.
The NASA/ESA Hubble Space Telescope has captured a beautiful galaxy that, with its reddish and yellow central area, looks rather like an explosion from a Hollywood movie. The galaxy, called NGC 5010, is in a period of transition. The aging galaxy is moving on from life as a spiral galaxy, like our Milky Way, to an older, less defined type called an elliptical galaxy. In this in-between phase, astronomers refer to NGC 5010 as a lenticular galaxy, which has features of both spirals and ellipticals.
NGC 5010 is located around 140 million light-years away in the constellation of Virgo (The Virgin). The galaxy is oriented sideways to us, allowing Hubble to peer into it and show the dark, dusty, remnant bands of spiral arms. NGC 5010 has notably started to develop a big bulge in its disk as it takes on a more rounded shape.
Most of the stars in NGC 5010 are red and elderly. The galaxy no longer contains all that many of the fast-lived blue stars common in younger galaxies that still actively produce new populations of stars.
Much of the dusty and gaseous fuel needed to create fresh stars has already been used up in NGC 5010. Over time, the galaxy will grow progressively more “red and dead,” as astronomers describe elliptical galaxies.
Hubble’s Advanced Camera for Surveys snapped this image in violet and infrared light.
Credit: ESA/Hubble & NASA
Visible in the constellation of Andromeda, NGC 891 is located approximately 30 million light-years away from Earth. The NASA/ESA Hubble Space Telescope turned its powerful wide field Advanced Camera for Surveys towards this spiral galaxy and took this close-up of its northern half. The galaxy’s central bulge is just out of the image on the bottom left.
The galaxy, spanning some 100,000 light-years, is seen exactly edge-on, and reveals its thick plane of dust and interstellar gas. While initially thought to look like our own Milky Way if seen from the side, more detailed surveys revealed the existence of filaments of dust and gas escaping the plane of the galaxy into the halo over hundreds of light-years. They can be clearly seen here against the bright background of the galaxy halo, expanding into space from the disk of the galaxy.
Astronomers believe these filaments to be the result of the ejection of material due to supernovae or intense stellar formation activity. By lighting up when they are born, or exploding when they die, stars cause powerful winds that can blow dust and gas over hundreds of light-years in space.
A few foreground stars from the Milky Way shine brightly in the image, while distant elliptical galaxies can be seen in the lower right of the image.
NGC 891 is part of a small group of galaxies bound together by gravity.
A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Nick Rose. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public.
Read more: www.nasa.gov