Posted on by Fraser Cain

Galileo Plunges Into Jupiter

Image credit: NASA/JPL

NASA’s Galileo spacecraft was intentionally crashed into Jupiter on Sunday, ending 14 years of service to science and exploration. The spacecraft entered Jupiter’s thick atmosphere and disintegrated at 1857 GMT (2:57pm EDT), but the last signals arrived at Earth nearly an hour later because of the great distance to Jupiter. At the end of its mission, Galileo lacked the fuel to escape the Jovian system so scientists decided to crash it into Jupiter to avoid contaminating any potential life on Europa, which is believed to have liquid water oceans under a thick sheet of ice.

The Galileo spacecraft’s 14-year odyssey came to an end on Sunday, Sept. 21, when the spacecraft passed into Jupiter’s shadow then disintegrated in the planet’s dense atmosphere at 11:57 a.m. Pacific Daylight Time. The Deep Space Network tracking station in Goldstone, Calif., received the last signal at 12:43:14 PDT. The delay is due to the time it takes for the signal to travel to Earth.

Hundreds of former Galileo project members and their families were present at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., for a celebration to bid the spacecraft goodbye.

“We learned mind-boggling things. This mission was worth its weight in gold,” said Dr. Claudia Alexander, Galileo project manager.

Having traveled approximately 4.6 billion kilometers (about 2.8 billion miles), the hardy spacecraft endured more than four times the cumulative dose of harmful jovian radiation it was designed to withstand. During a previous flyby of the moon Amalthea in November 2002, flashes of light were seen by the star scanner that indicated the presence of rocky debris circling Jupiter in the vicinity of the small moon. Another measurement of this area was taken today during Galileo’s final pass. Further analysis may help confirm or constrain the existence of a ring at Amalthea’s orbit.

“We haven’t lost a spacecraft, we’ve gained a steppingstone into the future of space exploration,” said Dr. Torrance Johnson, Galileo project scientist.

The spacecraft was purposely put on a collision course with Jupiter because the onboard propellant was nearly depleted and to eliminate any chance of an unwanted impact between the spacecraft and Jupiter’s moon Europa, which Galileo discovered is likely to have a subsurface ocean. Without propellant, the spacecraft would not be able to point its antenna toward Earth or adjust its trajectory, so controlling the spacecraft would no longer be possible. The possibility of life existing on Europa is so compelling and has raised so many unanswered questions that it is prompting plans for future spacecraft to return to the icy moon.

Galileo was launched from the cargo bay of Space Shuttle Atlantis in 1989. The exciting list of discoveries started even before Galileo got a glimpse of Jupiter. As it crossed the asteroid belt in October 1991, Galileo snapped images of Gaspra, returning the first ever close-up image of an asteroid. Less then a year later, the spacecraft got up close to yet another asteroid, Ida, revealing it had its own little “moon,” Dactyl, the first known moon of an asteroid. In 1994 the spacecraft made the only direct observation of a comet impacting a planet– comet Shoemaker-Levy 9’s collision with Jupiter.

The descent probe made the first in-place studies of the planet’s clouds and winds, and it furthered scientists’ understanding of how Jupiter evolved. The probe also made composition measurements designed to assess the degree of evolution of Jupiter compared to the Sun.

Galileo made the first observation of ammonia clouds in another planet’s atmosphere. It also observed numerous large thunderstorms on Jupiter many times larger than those on Earth, with lightning strikes up to 1,000 times more powerful than on Earth. It was the first spacecraft to dwell in a giant planet’s magnetosphere long enough to identify its global structure and to investigate the dynamics of Jupiter’s magnetic field. Galileo determined that Jupiter’s ring system is formed by dust kicked up as interplanetary meteoroids smash into the planet’s four small inner moons. Galileo data showed that Jupiter’s outermost ring is actually two rings, one embedded within the other.

Galileo extensively investigated the geologic diversity of Jupiter’s four largest moons: Ganymede, Callisto, Io and Europa. Galileo found that Io’s extensive volcanic activity is 100 times greater than that found on Earth. The moon Europa, Galileo unveiled, could be hiding a salty ocean up to 100 kilometers (62 miles) deep underneath its frozen surface containing about twice as much water as all the Earth’s oceans. Data also showed Ganymede and Callisto may have a liquid-saltwater layer. The biggest discovery surrounding Ganymede was the presence of a magnetic field. No other moon of any planet is known to have one.

The prime mission ended six years ago, after two years of orbiting Jupiter. NASA extended the mission three times to continue taking advantage of Galileo’s unique capabilities for accomplishing valuable science. The mission was possible because it drew its power from two long-lasting radioisotope thermoelectric generators provided by the Department of Energy.

“The mission was a testimonial to the persistence of NASA even through tremendous challenges. It was a phenomenal mission,” said Sean O’Keefe, NASA administrator.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Early Supernovae Seeded the Universe With Elements

Image source: CfA

According to cosmologists, the early Universe only had a mixture of hydrogen, helium and other lighter elements, but none of the heaver elements required for life – like carbon. From the original gasses, giant stars formed – some were 200 times larger than our Sun – lived for a brief time, often just a few million years. These giant stars converted up to 50% of their material into heaver elements, mostly iron, before exploding violently as supernovae. The James Webb telescope, due for launch after 2011 will be so sensitive it should be able to look back to watch these supernovae happening.

The early universe was a barren wasteland of hydrogen, helium, and a touch of lithium, containing none of the elements necessary for life as we know it. From those primordial gases were born giant stars 200 times as massive as the Sun, burning their fuel at such a prodigious rate that they lived for only about 3 million years before exploding. Those explosions spewed elements like carbon, oxygen and iron into the void at tremendous speeds. New simulations by astrophysicists Volker Bromm (Harvard-Smithsonian Center for Astrophysics), Naoki Yoshida (National Astronomical Observatory of Japan) and Lars Hernquist (CfA) show that the first, “greatest generation” of stars spread incredible amounts of such heavy elements across thousands of light-years of space, thereby seeding the cosmos with the stuff of life.

This research is posted online at http://arxiv.org/abs/astro-ph/0305333 and will be published in an upcoming issue of The Astrophysical Journal Letters.

“We were surprised by how violent the first supernova explosions were,” says Bromm. “A universe that was in a pristine state of tranquility was rapidly and irreversibly transformed by a colossal input of energy and heavy elements, setting the stage for the long cosmic evolution that eventually led to life and intelligent beings like us.”

Approximately 200 million years after the Big Bang, the universe underwent a dramatic burst of star formation. Those first stars were massive and fast-burning, quickly fusing their hydrogen fuel into heavier elements like carbon and oxygen. Nearing the end of their lives, desperate for energy, those stars burned carbon and oxygen to form heavier and heavier elements until reaching the end of the line with iron. Since iron cannot be fused to create energy, the first stars then exploded as supernovae, blasting the elements that they had formed into space.

Each of those first giant stars converted about half of its mass into heavy elements, much of it iron. As a result, each supernova hurled up to 100 solar masses of iron into the interstellar medium. The death throes of each star added to the interstellar bounty. Hence, by the remarkably young age of 275 million years, the universe was substantially seeded with metals.

That seeding process was aided by the structure of the infant universe, where small protogalaxies less than one-millionth the mass of the Milky Way crammed together like people on a crowded subway car. The small sizes of and distances between those protogalaxies allowed an individual supernova to rapidly seed a significant volume of space.

Supercomputer simulations by Bromm, Yoshida, and Hernquist showed that the most energetic supernova explosions sent out shock waves that flung heavy elements up to 3,000 light-years away. Those shock waves swept huge amounts of gas into intergalactic space, leaving behind hot “bubbles,” and triggered new rounds of star formation.

Supernova expert Robert Kirshner (CfA) says, “Today this is a fascinating theory, based on our best understanding of how the first stars worked. In a few years, when we build the James Webb Space Telescope, the successor to the Hubble Space Telescope, we should be able to see these first supernovae and test Volker’s ideas. Stay tuned!”

Lars Hernquist notes that the second generation of stars contained heavy elements from the first generation – seeds from which rocky planets like Earth could grow. “Without that first, ‘greatest generation’ of stars, our world would not exist.”

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release

Posted on by Fraser Cain

SMART-1 Launch Date Set

Image credit: ESA

The launch date for the European Space Agency’s SMART-1 spacecraft has been set for early morning of September 28. Earlier this week the spacecraft was attached to the top of an Ariane 5 rocket at the Kourou spaceport in French Guiana. When it finally does get into space, SMART-1 will use its ion engine to slowly spiral away from the Earth until it gets captured by the gravity of the Moon. Once its in orbit around the Moon, it will map the chemical composition of the surface with greater detail than ever done before. It will also search for evidence of water ice at the Moon’s south pole.

The launch date for ESA’s SMART-1 mission to the Moon is confirmed as during the night of 27-28 September 2003.

The ‘launch window’ will be 8:02 p.m. to 8:21 p.m. on Saturday, 27 September, local time in Kourou, French Guiana, and 1:02 a.m. to 1:21 a.m. on Sunday, 28 September, CEST.

Earlier this week, the SMART-1 spacecraft completed the first 30 metres of its trip to the Moon when it was put on board its Ariane 5 launcher at the Kourou spaceport in French Guiana.

As ESA scientists and engineers watched, the spacecraft looked very small, with its Ariane 5 mounting adapter, when it was raised the 30 metres up to the top of the launcher inside the Final Assembly Building (BAF). Within an hour it was sitting on the rocket’s upper stage.

The spacecraft is pictured here being made ready for flight and having its solar panel array protection removed. The next step is to enclose the spacecraft with the 2.6-metre raising cylinder, which carries the second passenger satellite, E-Bird, on top of SMART-1.

Original Source: ESA News Release

Posted on by Fraser Cain

Shuttle’s Return to Flight Pushed Back to Summer

The return to flight of the space shuttle will probably be pushed back to midsummer according to NASA officials; not March as they had originally anticipated. The delay is being caused by the complexity of implementing the safety recommendations of the Columbia accident investigation, which called for additional cameras, day launches, and redesigns to several shuttle components. When Atlantis finally does launch with only four astronauts, its only purpose will be to test out the new safety improvements. It will dock with the International Space Station and allow the astronauts to test methods for finding and repairing damage to the shuttle’s exterior.

Posted on by Fraser Cain

China Will Help Develop the Galileo Network

Image credit: ESA

The European Union announced on Thursday that China will play a role in the development of the Galileo constellation of satellites, which are designed to provide a similar solution as the US-based Global Positioning System. The exact commitments from China haven’t been detailed yet, but the two groups have set up a training, cooperation, and information centre for satellite navigation in China at Beijing University. Galileo will be built with 30 navigation satellites to provide complete global coverage – it’s expected to be fully operational by 2008.

Europe and China share a common interest in cooperating to bring the benefits of satellite navigation and Galileo in particular to transport, science, land management, disaster prevention and other user sectors.

Sharing research results, encouraging education, joint projects and industrial contacts are important means towards such goals.

In this context, the European Commission, the European Space Agency and the Chinese Ministry of Science and Technology have decided to establish a training, cooperation and information centre for satellite navigation in China. On the basis of bilateral discussions to date in the Europe-China Joint Technical Working Group, the decision has been taken to locate the centre at the renowned Beijing University.

The centre will be staffed initially by one or two experts supported by two administrative and technical assistants.

Mr F. Lamoureux, Director General for Energy and Transport at the European Commission, will inaugurate the centre together with Mr Shi Dinghuan, Secretary General of the Chinese Ministry of Science and echnology, at 11:00 on Friday 19 September in Beijing.

This will take place at the China-Europe Technical Training and Cooperation Centre, Room 323 ZhongGuanCun FangZheng Building, No 298, Chengfu Road, Haidian District (in front of the Beijing University East Gate).

The Galileo system will be built around 30 satellites (27 operational and three in reserve) stationed on three circular medium-Earth orbits at an altitude of 23 616 km and inclined at 56? to the equator. This configuration will provide excellent coverage of the entire planet. Two Galileo centres will be set up in Europe to control satellite operations and manage the navigation system.

Developed by ESA and the European Union on the basis of 50-50 cofinancing, Galileo will be a complete civil system, due to be operational from 2008, offering users in Europe, and throughout the world as well, a precise, secure satellite positioning service.

Original Source: ESA News Release

Posted on by Fraser Cain

SpaceDev Will Build SpaceshipOne Motor.

Image credit: Scaled

Scaled Composites announced today that it has selected San Diego-based SpaceDev to build the rocket engine for SpaceShipOne. The hybrid engine uses nitrous oxide and rubber, and was chosen for both safety and performance. SpaceShipOne is Scaled Composite’s entrant into the X-Prize; a $10 million prize to the first private company able to launch a 2-person crew to an altitude of 100 km. No future plans or launch dates have been announced but the spacecraft must complete a successful flight before the end of 2004 to claim the prize.

Four years ago, Scaled conducted a study of rocket engine technologies that were appropriate for its future manned sub-orbital spaceship design. The results of this study were that a hybrid configuration using nitrous oxide (liquid N2O) and HTPB (rubber) propellants would likely provide the safest solution with operating characteristics that would complement the intended mission.

In Jan 2000, Scaled defined a new integrated concept for the hybrid motor that allowed the entire propulsion system to be mounted to the spaceship by simple skirt flanges on the oxidizer tank. This concept, which cantilevers the case and nozzle directly to the tank, required an advanced all-composite design approach. By early 2001, Scaled had committed to developing the two main motor composite components in-house: The first is the nitrous oxide tank, a composite liner laid up onto titanium flanges, with a graphite over-wrap provided by Thiokol. The second is a unitized fuel case/nozzle component fabricated using a high-temperature composite insulator with a graphite/epoxy structure laid up onto an ablative nozzle supplied by AAE Aerospace.

In mid 2001, Scaled awarded contracts to two competing small businesses for the “rocket science”. Each company was independently responsible for the development of the motor’s ignition system, main control valve, injector, tank bulkheads, electronic controls, fill/dump/vent systems and fuel casting. The vendors, Environmental Aeroscience Corporation (eAc) of Miami and SpaceDev (SD) of San Diego, were also tasked with conducting the ground firing tests of their motor systems in Scaled’s test facility during the development phase.

In June 2002, Scaled selected eAc to supply the components at the tanks’ front end: the nitrous fill, vent and dump system components and associated plumbing. Both vendors continued the development of all the other propulsion components.

The ground firing development program started in November 2002 with a 15 second run by the SpaceDev team and ended early this month with a 90-second run by eAc. Both vendors demonstrated full design-duration firings during the nine-month development phase. All tests have exclusively used 100% flight hardware, with no boilerplate components and both vendors’ motor systems met the contracted performance. The tests validated the inherent safety of hybrid type motors, with no instances of structural failure, hot-gas breach, explosion or other anomaly that would have put SpaceShipOne in jeopardy.

Because both teams were so closely matched, and since both have developed satisfactory motors the process to select one of these vendors to enter the motor qualification and flight test phase was difficult. However, today, Scaled is pleased to announce that it has awarded the contract for propulsion support for the SpaceShipOne flight test phase to SpaceDev, of San Diego.

Scaled now looks forward to entering into the historic phase of private manned space flight.

Original Source: Scaled Composites News Release

Posted on by Fraser Cain

ESA’s View of Hurricane Isabel

Image credit: ESA

The European Space Agency is helping to track the movement of Hurricane Isabel using its ERS-2 spacecraft, and released this photo of the storm Thursday morning as it menaced the East Coast of the US. ERS-2 has also been gathering other information about the storm, including sea surface temperatures, wind and rainfall levels. Isabel is a Category 2 hurricane, and expected to make landfall in the early afternoon on Thursday in North Carolina.

As Hurricane Isabel converges on the US East Coast, a veteran ESA spacecraft has provided meteorologists with crucial insights into the underlying pressure system powering the storm.

An entire flotilla of satellites is being kept busy tracking Hurricane Isabel in visible and infrared light, as well as gathering additional measurements of local sea surface temperature, wind and rainfall levels. ESA spacecraft ERS-2 has made the picture more detailed still by discerning the wind speed and direction around the hurricane’s cloud and rain-wracked heart.

ERS-2 instruments include a C-band scatterometer, which works by sending a high-frequency radar pulse down to the ocean, then analysing the pattern of backscatter reflected back again. Scatterometers are particularly useful in measuring wind speed and direction at the sea surface, by detecting signature scatter from ripples on the water caused by wind.

ERS-2’s scatterometer is less sensitive than comparable space-based instrumentsto rain or bad weather, and can gather data both day and night. This makes it invaluable as an early detector of Atlantic storms ? especially in the current hurricane season.

The Isabel data was obtained mid-afternoon Wednesday at one of ESA?s ground stations in Gatineau Canada, then rapidly delivered to meteorology offices worldwide. At the Reading-based European Centre for Medium-Range Weather Forecasts (ECMWF), it was analysed against the surface wind pattern predicted by their existing software simulation of Isabel, run on powerful supercomputers.

“The ERS wind data is very valuable to us,” said Hans Hersbach of ECMWF. “It shows differences with our analysis, for instance a lack of inward wind flow into the centre. By assimilating the data into our analysis we improve our forecasting skills.

“The ESA scatterometer data was routinely assimilated into our analysis after 1997, until it become no longer available early this century. Now the service has been resumed we are making use of it once more.”

ESA’s ERS-2 has been in orbit since 1995, but the service from the scatterometer was interrupted in 2001. A degradation in attitude control prevented access to the data. Meteorologists lost a valuable window on the weather ? until this summer, when after two-and-a-half-years of effort, new processing software developed by the Belgian Royal Military Academy (RMA) compensated for the degradation and regained access to scatterometer measurements.

The software algorithm was installed in ground stations at Kiruna in Sweden, Maspalomas in the Canary Islands Gatineau in Canada as well as Frascati in Italy, with an additional installation planned for West Freugh in Scotland. The new service began at the end of August, just in time for Hurricane Isabel’s dramatic arrival.

To maintain future continuity of scatterometer coverage, a new more advanced scatterometer instrument called ASCAT is part of the payload for ESA?s MetOp mission, currently due to launch in 2005.

Inside a hurricane
Hurricanes are large powerful storms that rotate around a central area of extreme low pressure. They arise in warm tropical waters that transfer their heat to the air. The warmed air rises rapidly, in the process creating low pressure at the water surface. Winds begin rushing inwards and upwards around this low-pressure zone.

Currently classed at Category Two on the five-point Saffir-Simpson Hurricane scale, Isabel originated in the eastern Atlantic last week. It is currently moving northwest at only about 24 kilometres an hour but winds within it are rotating at about 160 km per hour. Meteorologists forecast the hurricane will make landfall in North Carolina on Thursday.

Original Source: ESA News Release

Posted on by Fraser Cain

Galileo’s Final Study of Jupiter

Image credit: NASA/JPL

We’re only days away until Galileo’s final plunge into Jupiter on September 21. Nearly out of fuel, the spacecraft was put onto a collision course with Jupiter to prevent it from accidentally crashing into Europa and potentially contaminating it with Earth-based bacteria. The entry point on Jupiter will be 1/4 of a degree south of its equator and it will strike the planet at 174,000 km/h – obviously it’ll be destroyed almost instantly. Scientists hope to retrieve every piece of data they can, but the radiation will intensify to immense levels as the spacecraft nears the planet, so it might not be possible.

In the end, the Galileo spacecraft will get a taste of Jupiter before taking a final plunge into the planet’s crushing atmosphere, ending the mission on Sunday, Sept. 21. The team expects the spacecraft to transmit a few hours of science data in real time leading up to impact.

The spacecraft has been purposely put on a collision course with Jupiter to eliminate any chance of an unwanted impact between the spacecraft and Jupiter’s moon Europa, which Galileo discovered is likely to have a subsurface ocean. The long-planned impact is necessary now that the onboard propellant is nearly depleted.

Without propellant, the spacecraft would not be able to point its antenna toward Earth or adjust its trajectory, so controlling the spacecraft would no longer be possible.

“It has been a fabulous mission for planetary science, and it is hard to see it come to an end,” said Dr. Claudia Alexander, Galileo project manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “After traversing almost 3 billion miles and being our watchful eyes and ears around Jupiter, we’re keeping our fingers crossed that, even in its final hour, Galileo will still give us new information about Jupiter’s environment.”

Although scientists are hopeful to get every bit of data back for analysis, the likelihood of getting anything is unknown because the spacecraft has already endured more than four times the cumulative dose of harmful jovian radiation it was designed to withstand. The spacecraft will enter an especially high-radiation region again as it approaches Jupiter.

Launched in the cargo bay of Space Shuttle Atlantis in 1989, the mission has produced a string of discoveries while circling the solar system’s largest planet, Jupiter, 34 times. Galileo was the first mission to measure Jupiter’s atmosphere directly with a descent probe and the first to conduct long-term observations of the jovian system from orbit.

It found evidence of subsurface liquid layers of salt water on Europa, Ganymede and Callisto and it examined a diversity of volcanic activity on Io. Galileo is the first spacecraft to fly by an asteroid and the first to discover a moon of an asteroid.

The prime mission ended six years ago, after two years of orbiting Jupiter. NASA extended the mission three times to continue taking advantage of Galileo’s unique capabilities for accomplishing valuable science. The mission was possible because it drew its power from two long-lasting radioisotope thermoelectric generators provided by the Department of Energy.

From launch to impact, the spacecraft has traveled 4,631,778,000 kilometers (about 2.8 billion miles).

Its entry point into the giant planet’s atmosphere is about 1/4 degree south of Jupiter’s equator. If there were observers floating along at the cloud tops, they would see Galileo streaming in from a point about 22 degrees above the local horizon. Streaming in could also be described as screaming in, as the speed of the craft relative to those observers would be 48.2 kilometers per second (nearly 108,000 miles per hour). That is the equivalent of traveling from Los Angeles to New York City in 82 seconds. In comparison, the Galileo atmospheric probe, aerodynamically designed to slow down when entering, and parachute gently through the clouds, first reached the atmosphere at a slightly more modest 47.6 kilometers per second (106,500 miles per hour).

“This is a very exciting time for us as we draw to a close on this historic mission and look back at its science discoveries. Galileo taught us so much about Jupiter but there is still much to be learned, and for that we look with promise to future missions,” said Dr. Charles Elachi, director of JPL.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Astronomers Find a Transparent Galaxy

Image credit: Hubble

It turns out that a collection of stars orbiting the Andromeda galaxy are actually the remnants of another galaxy being torn apart and consumed, according to new research from astronomers at Case University. They only realized it was a separate galaxy after charting the velocities of several of its stars. Astronomers failed to detect it before now because much of the galaxy is located in front of Andromeda’s bright galactic disk. The discovery will give astronomers further evidence to support the theory that smaller galaxies merge together to form larger, more complex galaxies.

Case Western Reserve University astronomers have announced the discovery of a new galaxy, termed Andromeda VIII. The new galaxy is so widespread and transparent that astronomers did not suspect its existence until they mapped the velocity of stars thought to belong to the well-known and nearby large Andromeda spiral galaxy and found them to move independently of Andromeda.

Heather Morrison, Paul Harding and Denise Hurley-Keller of Case’s department of astronomy and George Jacoby of the WIYN Observatory, will report their discovery in an upcoming article in Astrophysical Journal Letters.

“This is particularly exciting because it allows us to watch the ongoing growth of the nearby Andromeda galaxy from smaller galaxies,” says Morrison.

The astronomers used Case’s Burrell Schmidt telescope and the 3.5m WIYN telescope to identify the galaxy. Both telescopes are located at Kitt Peak National Observatory near Tucson, Ariz. NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

The newly found galaxy is being torn apart into streams of stars, which leaves a trail of stars that are strung out along the new galaxy’s orbit around the Andromeda galaxy in the way a jet’s contrail shows its route. Andromeda is the nearest large spiral galaxy to our own Milky Way galaxy two million light years away. It is visible as a hazy glowing object to the naked eye in a dark sky in the northern hemisphere and is found in the constellation of Andromeda.

Discovered over 1,000 years ago by the Persian astronomer Azophi Al-Sufi, Andromeda is a member of the Local Group of approximately 30 galaxies in the Milky Way’s celestial backyard.

In early August, Morrison finished analyzing the data of these stars from the Andromeda celestial neighborhood. “I was amazed to find a new dwarf galaxy orbiting Andromeda. It is a ‘see-thru’ galaxy, which was only discovered once we obtained velocity measurements for some of its stars, said Morrison.

She adds that the reason Andromeda VIII escaped detection was the fact that it is located in front of the bright regions of Andromeda’s galaxy disk.

Andromeda VIII’s total brightness is comparable to that of Andromeda’s well-known companion M32, a small nearby galaxy, but Andromeda VIII is spread over an area of the sky as much as ten times or more larger than M32. Its elongated shape is caused by Andromeda’s gravitational pull,
which has stretched it out due to the stronger gravity on the side nearest Andromeda.

Morrison and her collaborators also suggested that a very faint stream of stars, detected near the large Andromeda galaxy in 2001 by the Italian Astronmer R. A. Ibata and colleagues, was pulled off Andromeda VIII in an earlier passage around the parent galaxy. “Future research in this area should provide rich and fruitful results,” stated Morrison.

Theory has predicted for decades that galaxies are assembled in a “bottom-up” process, forming first as small galaxies that later merge to form large ones.

“Since 1994, when Ibata and colleagues announced the discovery of a new satellite in the process of being swallowed by the Milky Way, we have been able to see the process taking place in our own galaxy,” stated Morrison. “Now we find the same process in our nearest large neighbor.”

She adds that now it looks like Andromeda is even more inundated by small galaxies than the Milky Way. Ibata and colleagues have taken deep images of Andromeda which show a rich collection of star streams wreathed about the galaxy. Morrison and her colleagues have now identified the source of one of these star streams. They plan future observations to connect the different star streams with their progenitors, and thus learn more about the properties of the companion galaxy, the Andromeda galaxy and its elusive dark matter halo, the unseen matter that is suspected to be present in the universe.

The galaxy research was supported by a five-year National Science Foundation Early Career Development Award.

The Burrell Schmidt telescope is part of Case’s Warner and Swasey Observatory. The WIYN 3.5-meter telescope is a partnership of the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatory (NOAO). NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NSF News Release

Posted on by Fraser Cain

More Evidence for Dark Energy

Image credit: Hubble

Astronomers have studied the light from 11 new supernovae to help validate the evidence that some kind of “dark energy” is accelerating the Universe apart. The supernovae are a special type called Ia, which are known to be roughly the same brightness. By measuring their relative brightness, they can calculate how distant the Type Ia supernovae are. This latest data was gathered by an international team of astronomers using ground telescopes to provide followup targets for the Hubble Space Telescope. A new satellite is planned, called the SuperNova/Acceleration Probe, which will be able to discover thousands of supernova and track their explosions precisely.

A unique set of 11 distant Type Ia supernovae studied with the Hubble Space Telescope sheds new light on dark energy, according to the latest findings of the Supernova Cosmology Project (SCP), recently posted at http://www.arxiv.org/abs/astro-ph/0309368 and soon to appear in the Astrophysical Journal.

Light curves and spectra from the 11 distant supernovae constitute “a strikingly beautiful data set, the largest such set collected solely from space,” says Saul Perlmutter, an astrophysicist at Lawrence Berkeley National Laboratory and leader of the SCP. The SCP is an international collaboration of researchers from the United States, Sweden, France, the United Kingdom, Chile, Japan, and Spain.

Type Ia supernovae are among astronomy’s best “standard candles,” so similar that their brightness provides a dependable gauge of their distance, and so bright they are visible billions of light years away.

The new study reinforces the remarkable discovery, announced by the Supernova Cosmology Project early in 1998, that the expansion of the universe is accelerating due to a mysterious energy that pervades all space. That finding was based on data from over three dozen Type Ia supernovae, all but one of them observed from the ground. A competing group, the High-Z Supernova Search Team, independently announced strikingly consistent results, based on an additional 14 supernovae, also predominantly observed from the ground.

Because the Hubble Space Telescope (HST) is unaffected by the atmosphere, its images of supernovae are much sharper and stronger and provide much better measurements of brightness than are possible from the ground. Robert A. Knop, assistant professor of physics and astronomy at Vanderbilt University in Nashville, Tenn., led the Supernova Cosmology Project’s data analysis of the 11 supernovae studied with the HST and coauthored the Astrophysical Journal report with the 47 other members of the SCP.

“The HST data also provide a strong test of host-galaxy extinction,” Knop says, referring to concerns that measurements of the true brightness of supernovae could be thrown off by dust in distant galaxies, which might absorb and scatter their light. But dust would also make a supernova’s light redder, much as our sun looks redder at sunset because of dust in the atmosphere. Because the data from space show no anomalous reddening with distance, Knop says, the supernovae “pass the test with flying colors.”

“Limiting such uncertainties is crucial for using supernovae ? or any other astronomical observations ? to explore the nature of the universe,” says Ariel Goobar, a member of SCP and a professor of particle astrophysics at Stockholm University in Sweden. The extinction test, says Goobar, “eliminates any concern that ordinary host-galaxy dust could be a source of bias for these cosmological results at high-redshifts.” (See What is Host-Galaxy Extinction?)

The term for the mysterious “repulsive gravity” that drives the universe to expand ever faster is dark energy. The new data are able to provide much tighter estimates of the relative density of matter and dark energy in the universe: under straightforward assumptions, 25 percent of the composition of the universe is matter of all types, and 75 percent is dark energy. Moreover, the new data provide a more precise measure of the “springiness” of the dark energy, the pressure that it applies to the universe’s expansion per unit of density.

Among the numerous attempts to explain the nature of dark energy, some are allowed by these new measurements ? including the cosmological constant originally proposed by Albert Einstein ? but others are ruled out, including some of the simplest models of the theories known as quintessence. (See What is Dark Energy?)

High-redshift supernovae are the best single tool for measuring the properties of dark energy ? and eventually determining what dark energy is. As supernova studies with the HST demonstrate, the best place to study high-redshift supernovae is with a telescope in space, unaffected by the atmosphere.

Nevertheless, “to make the best use of a telescope in space, it’s essential to make the best use of the finest telescopes on the ground,” says SCP member Chris Lidman of the European Southern Observatory.

For the supernovae in the present study, the SCP team invented a strategy whereby the Hubble Space Telescope could quickly respond to discoveries made from the ground, despite the need to schedule HST time long in advance. Working together, the SCP and the Space Telescope Science Institute implemented the strategy to superb effect.

The current study, based on HST observations of 11 supernovae, points the way to the next generation of supernova research: in the future, the SuperNova/Acceleration Probe, or SNAP satellite, will discover thousands of Type Ia supernovae and measure their spectra and their light curves from the earliest moments, through maximum brightness, until their light has died away.

SCP’s Perlmutter is now leading an international group of collaborators based at Berkeley Lab who are developing SNAP with the support of the U.S. Department of Energy’s Office of Science. It may be that the best candidate for a correct theory of dark energy will be identified soon after SNAP begins operating. A world of new physics will open as a result.

“New constraints on omega-m, omega-lambda, and w from an independent set of eleven high-redshift supernovae observed with the HST,” by Robert A. Knop and 47 others (the Supernova Cosmology Project), will appear in the Astrophysical Journal and is currently available online at http://www.arxiv.org/abs/astro-ph/0309368.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Original Source: Berkeley News Release