Universe Today

Image credit: Hubble

NASA provided the first pictures today from the newly refurbished Hubble Space Telescope. Among the four new images unveiled to the public today included colliding galaxies, and several nebulas. The Advanced Cameral for Surveys was installed by the crew of the space shuttle Atlantis just a few months ago, and seems to be working well. Operators expect it will be ten times more efficient than the observatory’s previous camera – so far, so good.

“Remarkable, breathtaking” are words jubilant astronomers are using to describe the first four views of the universe taken by the Hubble Space Telescope’s new Advanced Camera for Surveys, released by NASA today.

The new camera was installed on Hubble by astronauts during a shuttle mission last March, the fourth Hubble Space Telescope servicing mission. During five of the most challenging spacewalks ever attempted, the crew successfully upgraded the orbiting telescope with the new camera, a new power unit, new solar arrays and an experimental cooling unit for an infrared camera. Hubble managers say the orbiting telescope has been operating superbly since the servicing mission.

“Today marks the beginning of a new era of exploration with Hubble,” said Dr. Ed Weiler, Associate Administrator for Space Science at NASA Headquarters, Washington. “Our team of scientists and engineers on the ground and the astronauts in space once again did the impossible. After 12 years in space, Hubble not only was given a major overhaul, its new camera has already shown us that, even after 12 years of great science and astounding images, we haven’t seen anything yet.”

Among the suite of four “suitable-for-framing” Advanced Camera for Surveys (ACS) science-demonstration pictures released today is a stunning view of a colliding galaxy, dubbed the “Tadpole,” located 420 million light-years away. Unlike textbook images of stately galaxies, the “Tadpole” ? with a long tail of stars ? captures the essence of a dynamic, restless and violent universe, looking like a runaway pinwheel firework.

“The ACS is opening a wide new window onto the universe. These are among the best images of the distant universe humans have ever seen,” said astronomer Holland Ford of Johns Hopkins University in Baltimore, lead scientist in the camera’s seven-year development.

The camera’s tenfold increase in efficiency will open up much anticipated new capability for discovery. “ACS will allow us to push back the frontier of the early universe. We will be able to enter the ‘twilight zone’ period when galaxies were just beginning to form out of the blackness following the cooling of the universe from the big bang,” said Ford.

The ACS is a camera of superlatives. It is expected to surpass the sensitivity of the largest ground-based telescope to eventually see the very faintest objects ever recorded. The camera delivers a panoramic crispness comparable to that of a wide-screen movie, containing 16 million picture elements (megapixels) per image. By comparison, digital photos from typical consumer cameras are 2 to 4 megapixels.

The ACS image of the Tadpole illustrates the dramatic gains over the Wide Field Planetary Camera 2 resulting from doubling the area and resolution, and demonstrates a five- fold improvement in sensitivity. An unexpected bonus is the enormous number of galaxies in the new Hubble image beyond the Tadpole galaxy, giving it an appearance like the galaxy- filled Hubble Deep Field (HDF) image, taken in 1995. However, the ACS picture was taken in one-twelfth the time it took for the original HDF. Like the Hubble Deep Field, the ACS galaxies contain myriad shapes that are snapshots of galaxies throughout the universe’s 13 billion-year evolution. The ACS images are so sharp astronomers can identify “building blocks” of galaxies, colliding galaxies and extremely distant galaxies in the field ? an exquisite sampler of galaxies.

“The ACS will let us obtain the deepest image of the universe for the foreseeable future,” added astronomer Garth Illingworth of the University of California, Lick Observatory, Santa Cruz, the deputy leader for the camera team.

The other pictures include a stunning collision between two spiral galaxies, dubbed “the Mice,” that presage what might happen to our own Milky Way several billion years in the future when it collides with the neighboring galaxy in the constellation Andromeda. Computer simulations, made by Joshua Barnes of the University of Hawaii and John Hibbard of the National Radio Astronomy Observatory, show that we are seeing the collision of the Mice approximately 160 million years after their closest encounter. Running the simulations forward in time shows that the two galaxies will eventually merge. A similar fate may await the Milky Way and the Andromeda galaxy.

Looking closer to home, ACS imaged the “Cone Nebula,” a craggy-looking mountaintop of cold gas and dust that is a cousin to Hubble’s iconic “pillars of creation” in the Eagle Nebula, photographed in 1995.

Peering into a celestial maternity ward called the M17 Swan Nebula, the ACS revealed a watercolor fantasy-world tapestry of vivid colors and glowing ridges of gas. Embedded in this crucible of star creation are embryonic planetary systems.

In addition to the ACS, spacewalking astronauts installed a new high-tech mechanical “refrigerator” on Hubble during the servicing mission. This “cryocooler” has successfully pumped most of the heat out of the interior of the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), achieving and maintaining to within a few hundredths of one degree the target temperature for neon gas passing through the instrument of 70 degrees Kelvin (minus 203 degrees Centigrade or minus 333 degrees Fahrenheit).

Engineers are now in the process of checking out the operation of the resuscitated NICMOS instrument. By early June, scientists expect to release the first astronomical images taken with the NICMOS since 1998, when it was still being cooled by a rapidly depleting block of solid nitrogen ice.

The new rigid solar arrays, working with the new Power Control Unit, are generating 27 percent more electrical power than the previous arrays. This doubles the electrical power that can be allocated to the scientific instruments on Hubble. The new reaction wheel is operating normally. Nearly a month ago, the Space Telescope Imaging Spectrograph and the Wide Field and Planetary Camera 2 resumed science observations.

“This servicing mission has turned out to be an extraordinary success,” said Preston Burch, Hubble Project Manager at NASA’s Goddard Space Flight Center in Greenbelt, Md. “It was the most difficult and complicated Hubble servicing mission attempted to date and our observatory came through it with flying colors.”

Image credit: Hubble

Thanks to the Hubble Space Telescope, astronomers are using ancient stars in the Milky Way to come up with an independent estimate about the age of the Universe. In the past, astronomers have calculated this age using its rate of expansion, and pegged it between 13-14 billion years old. Under this new method, the astronomers targeted ancient white dwarf stars which cool down at a very predictable rate. These stars were formed near the beginning of the Universe, and the astronomers were able to estimate that they are between 12-13 billion years old. Close enough.

Pushing the limits of its powerful vision, NASA’s Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy. These extremely old, dim “clockwork stars” provide a completely independent reading on the age of the universe without relying on measurements of the expansion of the universe.

The ancient white dwarf stars, as seen by Hubble, turn out to be 12 to 13 billion years old. Because earlier Hubble observations show that the first stars formed less than 1 billion years after the universe’s birth in the big bang, finding the oldest stars puts astronomers well within arm’s reach of calculating the absolute age of the universe.

Though previous Hubble research sets the age of the universe at 13 to 14 billion years based on the rate of expansion of space, the universe’s birthday is such a fundamental and profound value that astronomers have long sought other age-dating techniques to cross-check their conclusions. “This new observation short-circuits getting to the age question, and offers a completely independent way of pinning down that value,” says Harvey Richer of the University of British Columbia, Canada.

The new age-dating observations were done by Richer and colleagues by using Hubble to go hunting for elusive ancient stars hidden inside a globular star cluster located 5,600 light-years away in the constellation Scorpius. The results are to be published in the Astrophysical Journal Letters.

Conceptually, the new age-dating observation is as elegantly simple as estimating how long ago a campfire was burning by measuring the temperature of the smoldering coals. For Hubble, the “coals” are white dwarf stars, the burned out remnants of the earliest stars that formed in our galaxy.

Hot, dense spheres of carbon “ash” left behind by the long-dead star’s nuclear furnace, white dwarfs cool down at a predictable rate ? the older the dwarf, the cooler it is, making it a perfect “clock” that has been ticking for almost as long as the universe has existed.

This approach has been recognized as more reliable than age-dating the oldest stars still burning by nuclear fusion, which relies on complex models and calculations about how a star burns its nuclear fuel and ages. White dwarfs are easier to age-date because they are simply cooling, but the trick has always been finding the dimmest and hence longest-running “clocks.”

As white dwarfs cool they grow fainter, and this required that Hubble take many snapshots of the ancient globular star cluster M4. The observations amounted to nearly eight days of exposure time over a 67-day period. This allowed for even fainter dwarfs to become visible, until at last the coolest ? and oldest ? dwarfs were seen. These stars are so feeble (at 30th magnitude ? which is considerably fainter than originally anticipated for any Hubble telescope imaging with the original cameras), they are less than one-billionth the apparent brightness of the faintest stars that can be seen by the naked eye.

Globular clusters are the first pioneer settlers of the Milky Way. Many coalesced to build the hub of our galaxy and formed billions of years before the appearance of the Milky Way’s magnificent pinwheel disk (as further confirmed by Richer’s observations). Today 150 globular clusters survive in the galactic halo. The globular cluster M4 was selected because it is the nearest to Earth, so the intrinsically feeblest white dwarfs are still apparently bright enough to be picked out by Hubble.

In 1928, Edwin Hubble’s measurements of galaxies made him realize that the universe was uniformly expanding, which meant the universe had a finite age that could be estimated by mathematically “running the expansion backward.” Edwin Hubble first estimated the universe was only 2 billion years old. Uncertainties over the true expansion rate led to a spirited debate in the late 1970s, with estimates ranging from 8 billion to 18 billion years. Estimates of the ages of the oldest normal “main-sequence” stars were at odds with the lower value, since stars could not be older than the universe itself.

In 1997 Hubble astronomers broke this impasse by triumphantly announcing a reliable age for the universe, calculated from a very precise measurement of the expansion rate. The picture soon got more complicated when astronomers using Hubble and ground-based observatories discovered the universe was not expanding at a constant rate, but accelerating due to an unknown repulsive force termed “dark energy.” When dark energy is factored into the universe’s expansion history, astronomers arrive at an age for the universe of 13-14 billion years. This age is now independently verified by the ages of the “clockwork” white dwarfs measured by Hubble.

Original Source: Hubble News Release