Category: Hubble

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

Image credit: NASA

The Hubble Space Telescope’s latest task is to track down elusive Pluto-like objects that lurk at the very edge of our Solar System – many of which seem to travel in pairs like Pluto and its moon Charon. These objects are classified as Kuiper Belt Objects (KBO) and can be found in a vast belt past Neptune. So far, 1% of KBOs have been found to be binary systems, a fact which puzzles astronomers.

NASA’s Hubble Space Telescope is hot on the trail of an intriguing new class of solar system object that might be called a Pluto “mini-me” ? dim and fleeting objects that travel in pairs in the frigid, mysterious outer realm of the solar system called the Kuiper Belt.

In results published today in the journal Nature, a team of astronomers led by Christian Veillet of the Canada-France-Hawaii Telescope Corporation (CFHT) in Kamuela, Hawaii, is reporting the most detailed observations yet of the Kuiper Belt object (KBO) 1998 WW31, which was discovered four years ago and found to be a binary last year by the CFHT.

Pluto and its moon Charon and countless icy bodies known as KBOs inhabit a vast region of space called the Kuiper Belt. This ‘junkyard’ of material left over from the solar system’s formation extends from the orbit of Neptune out to 100 times as far as the Earth is from the Sun (which is about 93 million miles) and is the source of at least half of the short-period comets that whiz through our solar system. Only recently have astronomers found that a small percentage of KBOs are actually two objects orbiting around each other, called binaries.

“More than one percent of the approximately 500 known KBOs are indeed binary: a puzzling fact for which many explanations will be proposed in what is going to be a very exciting and rapidly evolving field of research in the coming years,” says Veillet.

Hubble was able to measure the total mass of the pair based on their mutual 570-day orbit (a technique Isaac Newton used 400 years ago to estimate the mass of our Moon). The ‘odd-couple’ 1998 WW31 together are about 5,000 (0.0002) times less massive than Pluto and Charon.

Like a pair of waltzing skaters, the binary KBOs pivot around a common center of gravity. The orbit of 1998 WW31 is the most eccentric ever measured for any binary solar system object or planetary satellite. Its orbital distance varies by a factor of ten, from 2,500 to 25,000 miles (4,000 to 40,000 kilometers). It is difficult to determine how KBOs wind up traveling in pairs. They may have formed that way, born like twins, or may be produced by collisions where a single body is split in two.

Ever since the first KBO was discovered in 1992, astronomers have wondered how many KBOs may be binaries, but it was generally assumed that the observations would be too difficult for most telescopes. However, the insights to be gained from study of binary KBOs would be significant: measuring binary orbits provide estimates of KBO masses, and mutual eclipses of the binary allow astronomers to determine individual sizes and densities. Assuming some fraction of KBOs should be binary – just as has been discovered in the asteroid belt – astronomers eventually began to search for gravitationally entwined pairs of KBOs.

Then, finally, exactly a year ago on April 16, 2001, Veillet and collaborators announced the first discovery of a binary KBO: 1998 WW31. Since then, astronomers have reported the discoveries of six more binary KBOs. “It’s amazing that something that seems so hard to do and takes many years to accomplish can then trigger an avalanche of discoveries,” says Veillet. Four of those discoveries were made with the Hubble Space Telescope: two were discovered with a program led by Michael Brown of the California Institute of Technology in Pasadena, CA, and two more with a program led by Keith Noll of the Space Telescope Science Institute in Baltimore, MD. The sensitivity and resolution of Hubble is ideal for studying binary KBOs because the objects are so faint and so close together.

The Kuiper Belt is one of the last big missing puzzle pieces to understanding the origin and evolution of our solar system and planetary systems around other stars. Dust disks seen around other stars could be replenished by collisions among Kuiper Belt-type objects, which seems to be common among stars. These collisions offer fundamental clues to the birth of planetary systems.

Original Source: Hubble News Release

After three weeks of tests, NASA controllers have given the newly upgraded Hubble Space Telescope a clean bill of health. Initial tests are largely complete; however, calibrations of the observatory’s instruments are expected to continue for another two months. Routine science observations have now resumed using the telescope’s Imaging Spectrograph and the Wide Field and Planetary Camera 2.

After three weeks of in-orbit checkout, following its deployment from Space Shuttle Columbia on March 9, the Hubble Space Telescope has been declared healthy and fit by engineers and scientists at NASA’s Goddard Space Flight Center in Greenbelt, Md., and the Space Telescope Science Institute in Baltimore.

Initial checkout of the spacecraft and instruments has largely been completed. However, the calibration process for the instruments will continue for another two months. The new rigid solar arrays, coupled with the new Power Control Unit, are working perfectly, generating 27 percent more electrical power than the old arrays. This increase in power roughly doubles the power available to the scientific instruments. The new reaction wheel is operating normally.

The powerful new Advanced Camera for Surveys (ACS) is now undergoing its final optical alignment and focus checks. The image quality of individual stars observed in a standard calibration field is excellent. The Advanced Camera’s light-sensing detectors are also working very well. It is anticipated that the first Early Release Observations of astronomical targets taken with the Advanced Camera for Surveys will be available around the first week in May.

The new, high-tech mechanical cooler inserted by the Astronauts during SM3B has been working continuously and properly since March 18. The cooler?s intended purpose is to attempt to resuscitate the dormant Near-Infrared Camera and Multi-Object Spectrometer (NICMOS), which depleted its expendable solid nitrogen coolant in January 1999. Although this new ?refrigerator?, dubbed the NICMOS Cooling System (NCS), has been reliably generating the amount of cooling power expected, Hubble engineers report that the NICMOS instrument is cooling down more slowly than originally expected. Because it will take longer to reach the proper operating temperature, below approximately 80 degrees Kelvin, the initial checkout and scientific observations with NICMOS will be delayed for several weeks.

Routine science observations have now resumed with the Space Telescope Imaging Spectrograph and the Wide Field and Planetary Camera 2, the two instruments that were operating on Hubble prior to Servicing Mission 3B. On another note, a gyro (Gyro 3) that had not been performing as well as it should prior to the mission resumed perfect operation after it was turned off and re-started while Hubble was in Columbia’s payload bay.

The Space Shuttle Columbia journeyed to the Hubble Space Telescope for the fourth servicing mission on March 1, 2002. During a series of five spacewalks, Astronauts installed new hardware and upgraded older systems, leaving the telescope better than ever. After a successful mission spanning 11 days in orbit, the shuttle landed safely on March 12 at Kennedy Space Center, Fla.

Original Source: NASA News Release

A new photo released from the Hubble Space Telescope shows how galaxy NGC 7673 is teeming with hot star nurseries. Located 150 million light years away in the constellation of Pegasus, each cluster in this new photograph contains thousands of infant stars burning at incredibly high temperatures. Astronomers aren’t sure why this galaxy is so active, but it could be because the galaxy collided with another millions of years ago.

Image credit: Hubble

Even though the Hubble Space Telescope is out of commission while it’s upgraded, older images are still being released to the public. This image, actually taken back in 1995, reveals how a bow shock has formed around a young, hot star located in the Orion Nebula. The star, LL Ori emits a powerful solar wind that collides with the slower moving gas of the Orion Nebula. This bow shock, similar to that found at the front of a boat, is formed where the two winds collide.

NASA’s Hubble Space Telescope continues to reveal various stunning and intricate treasures that reside within the nearby, intense star-forming region known as the Great Nebula in Orion. One such jewel is the bow shock around the very young star, 1998 WW31, featured in this Hubble Heritage image.

Named for the crescent-shaped wave made by a ship as it moves through water, a bow shock can be created in space when two streams of gas collide. LL Ori emits a vigorous solar wind, a stream of charged particles moving rapidly outward from the star. Our own Sun has a less energetic version of this wind that is responsible for auroral displays on the Earth.

The material in the fast wind from LL Ori collides with slow-moving gas evaporating away from the center of the Orion Nebula, which is located to the lower right in this Heritage image. The surface where the two winds collide is the crescent-shaped bow shock seen in the image.

Unlike a water wave made by a ship, this interstellar bow shock is a three-dimensional structure. The filamentary emission has a very distinct boundary on the side facing away from LL Ori, but is diffuse on the side closest to the star, a characteristic common to many bow shocks.

A second, fainter bow shock can be seen around a star near the upper right-hand corner of the Heritage image. Astronomers have identified numerous shock fronts in this complex star-forming region and are using this data to understand the many complex phenomena associated with the birth of stars.

This image was taken in February 1995 as part of the Hubble Orion Nebula mosaic. A close visitor in our Milky Way galaxy, the nebula is only 1,500 light-years from Earth. The filters used in this color composite represent oxygen, nitrogen, and hydrogen emissions.

Original Source: Hubble News Release

Image credit: NASA

During a seven and a half hour spacewalk today, astronauts James Newman and Michael Massimino installed the Advanced Camera for Surveys onto the Hubble Space Telescope – a camera system ten times more powerful than what Hubble had previously. This is the fourth of five spacewalks carried out by the Columbia crew, who are due to return back to Earth on March 12th. The next spacewalk is due for Friday.
Following today?s successful installation of the new Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, scientists will be able to see farther into our universe and with greater clarity and speed than ever before.

Columbia?s spacewalkers, Jim Newman and Mike Massimino, began the first science instrument upgrade of this servicing mission at 3 a.m. central time. The duo, with Newman on the shuttle?s robotic arm, began by removing the last of Hubble?s original science instruments, the Faint Object Camera to make room for the ACS. Newman and Massimino first opened Hubble?s aft shroud doors, removing the Faint Object Camera and temporarily stowing it at the edge of Columbia?s payload bay. After installing the ACS in the Hubble, Newman and Massimino stowed the old camera in the payload bay for its return to Earth.

Then Massimino, on the shuttle?s robotic arm, installed the Electronic Support Module in the aft shroud, with Newman?s assistance. That module will support a new experimental cooling system to be installed during tomorrow?s fifth and final scheduled spacewalk of the mission. That cooling system is designed to bring the telescope’s Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) back to life.

Finally, Newman and Massimino completed some remaining cleanup tasks from yesterday?s Power Control Unit installation.

During the first half of the spacewalk, mission specialist Nancy Currie operated the shuttle?s robotic arm, providing transportation to and from the various worksites on both the Hubble and in Columbia?s payload bay ? Commander Scott Altman then took over operation of the arm to maneuver Massimino through his tasks.

Fellow spacewalkers John Grunsfeld and Rick Linnehan worked from inside the shuttle to choreograph the spacewalk, as Altman and Pilot Duane Carey continued to provide photo and video documentation of the work.

Initial functional tests on the ACS and the electronics module conducted by the Space Telescope Operations Control Center in Greenbelt, Md. were both good. Functional tests of the telescope’s scientific instruments will not be completed, however, until after the telescope is released from Columbia and its aperture door is opened.

The crew is to begin its sleep period at 2:52 p.m. CST. The next STS-109 mission status report will be issued Thursday evening following crew wake-up, or as events warrant.

Original Source: NASA News Release

Spacewalking astronauts spent their second day outside the space shuttle Columbia on Tuesday, adding a second new solar array to the Hubble Space Telescope. During the 7-hour, 16-minute spacewalk, astronauts James Newman and Michael Massimino also replaced one of the telescope’s stabilizing gyroscopes. The newly installed solar arrays are smaller than the telescope’s previous arrays, but they actually provide 20% more power. Three more spacewalks are still planned.

The latest image released from the Hubble Space Telescope shows a spiral galaxy that seems to be rotating in the wrong direction. Astronomers expected that galaxy NGC 4622, located 111 million light-years away in the constellation Centaurus, should rotate counter-clockwise but it actually goes clockwise. It’s believed that the galaxy consumed a smaller companion galaxy recently which helped reverse its spin.