Category: Hubble

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The Hubble Space Telescope has uncovered a strong new line of evidence that galaxies are embedded in halos of dark matter. By looking at the Perseus galaxy cluster, Hubble discovered a large number of small galaxies that have remained intact while larger galaxies around them are being ripped apart by the gravitational tug of other galaxies. “We were surprised to find so many dwarf galaxies in the core of this cluster that were so smooth and round and had no evidence at all of any kind of disturbance,” said astronomer Christopher Conselice of the University of Nottingham, UK, and leader of the team that made the Hubble observations. “These dwarfs are very old galaxies that have been in the cluster for a long time. So if something was going to disrupt them, it would have happened by now. They must be very, very dark-matter-dominated galaxies.”

Observations by Hubble’s Advanced Camera for Surveys spotted 29 dwarf elliptical galaxies in the Perseus Cluster, located 250 million light-years away and one of the closest galaxy clusters to Earth. Of these galaxies, 17 are new discoveries.

Cosmologists estimate that dark matter comprises 23 percent of all energy in the cosmos. An equally mysterious “dark energy,” which drives galaxies apart, is thought to take up another 73 percent or so. The ordinary matter that we can see is believed to represent only four percent of the total mass of the Universe.

Because dark matter cannot be seen, astronomers detected its presence through indirect evidence. The most common method is by measuring the velocities of individual stars or groups of stars as they move randomly in the galaxy or as they rotate around the galaxy. The Perseus Cluster is too far away for telescopes to resolve individual stars and measure their motions. So Conselice and his team derived a new technique for uncovering dark matter in these dwarf galaxies by determining the minimum additional mass contribution from dark matter that the dwarfs must have to protect them from being disrupted by the strong, tidal pull of gravity from larger galaxies.

But these new images provide evidence that the undisturbed galaxies are enshrouded by a “cushion” of dark matter that protects them from being torn apart.

Source: HubbleSite

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The folks who run the Hubble Space Telescope have decided to ask for some help in choosing where to next point the world’s most famous telescope. People from around the planet can vote to select the next object the Hubble Space Telescope will view. The choices are six objects Hubble has never observed before. You can also enter a drawing to win one of 100 new Hubble pictures of the object that is chosen. The winning image will be released between April 2 and 5, during the IYA’s 100 Hours of Astronomy, a global astronomy event geared toward encouraging as many people as possible to experience the night sky. You need to vote by March 1 to swing Hubble toward your favorite target. So get over to the HubbleSite and vote!

The choices are two planetary nebulae (NGC 40 and NGC 6072), an emission nebula (NGC 6634), an edge-on spiral (NGC 4289), a spiral galaxy (NGC 5172 – seen above from the Sloan Digital Sky Survey) and interacting galaxies (Arp 274).

Sources: HubbleSite, Bad Astronomy

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A team of astronomers looking for pre-planetary nebulae using the Hubble Space Telescope instead came across some renegade stars screaming through space. These runaway stars are moving along at 50 km/s (112,000 miles an hour), and have traveled an estimated 160 light years from where they originated. “We think we have found a new class of bright, high-velocity stellar interlopers,” says astronomer Raghvendra Sahai from JPL. “Finding these stars is a complete surprise because we were not looking for them. When I first saw the images, I said ‘Wow. This is like a bullet speeding through the interstellar medium.’ Hubble’s sharp ‘eye’ reveals the structure and shape of these bow shocks.”

Just as a speedboat on a lake creates a wake, as these speedy stars plow through the interstellar “ocean” they create brilliant bow shocks as streams of matter flowing from the stars slam into the surrounding dense gas.

So far, 14 of these runaway stars have been found. What kind of stars are they? Astronomers can only estimate the ages, masses, and velocities of these renegade stars. The stars appear to be young — just millions of years old. Their ages are inferred from their strong stellar winds. Most star produce such winds either when they are very young or when they are dying, and Sahia said it is clear they are not dying. Massive dying stars produce flowing clouds of ionized gas around them and that type of gas is not around these interlopers and old stars are almost never found near dense interstellar clouds.

They appear to be medium-sized stars that are a few to eight times more massive than the sun.
The research team believes the interloper stars were dynamically ejected from their natal environments which were probably massive star clusters. There are two way this could have happened. One possible scenario is that a star in a binary system exploded as a supernova and the partner got kicked out. Another possibility is a collision between two binary star systems or a binary system and a third star. One or more of these stars could have picked up energy from the interaction and escaped the cluster.

Depending on their distance from Earth, the bullet-nosed bow shocks could be 100 billion to a trillion miles wide (the equivalent of 17 to 170 solar system diameters, measured out to Neptune’s orbit). The bow shocks indicate that the stars are traveling fast, more than 112,000 miles an hour (more than 180,000 kilometers an hour) with respect to the dense gas they are plowing through, which is roughly five times faster than typical young stars.

Runaway stars have been seen before. The Infrared Astronomical Satellite (IRAS), which performed an all-sky infrared survey in 1983, spied a few similar-looking objects. The first observation of these objects was in the late 1980s. But those stars produced much larger bow shocks than the stars in the Hubble study, suggesting that they are more massive stars with more powerful stellar winds.

“The stars in our study are likely the lower-mass and/or lower-speed counterparts to the massive stars with bow shocks detected by IRAS,” Sahai explains. “We think the massive runaway stars observed before were just the tip of the iceberg. The stars seen with Hubble may represent the bulk of the population, both because many more lower-mass stars inhabit the universe than higher-mass stars, and because a much larger number are subject to modest speed kicks.”

Astronomers have not spotted many of these stellar interlopers before because they are hard to find. “You don’t know where to look for them because you cannot predict where they will be,” Sahai says. “So all of them have been found serendipitously, including the 14 stars we found with Hubble.”

“One of the questions that these very showy encounters raise is what effect they have on the clouds,” says team member Mark Morris of the University of California, Los Angeles. “Is it an insignificant flash in the pan, or do the strong winds from these stars stir up the clouds and thereby slow down their evolution toward forming another generation of stars?”

Sahai and his team used Hubble’s Advanced Camera for Surveys to examine 35 objects that appeared as bright infrared sources in the IRAS archive. The team is planning follow-up studies to search for more interlopers, as well as study selected objects from this Hubble survey in greater detail in order to understand their effects on their environment.

Source: NASA, AAS Press Conference

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The Hubble Space Telescope serendipitously captured a mysterious burst of light on February 21, 2006. Over the next 100 days, the object, cataloged as SCP 06F6, brightened and then slowly faded. Astronomers do not know the object’s distance, so it can either be in our Milky Way galaxy or at a great astronomical distance, and the light-signature of this event does not match the behavior of a supernova or any previously observed astronomical transient phenomenon in the universe. It might represent an entirely new class of stellar phenomena that has previously gone undetected in the universe, said Kyle Barbary of the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, Calif.y researchers. “No one has been able to come up with a good explanation for this object” he said at a press conference at today’s American Astronomical Society meeting in Long Beach, California. (Read on for an outlandish explanation one scientist proposed!)

Astronomers commonly observe intense flashes of light from a variety of stellar explosions and outbursts, such as novae and supernovae. But the rise and fall in brightness has a signature that simply has never been recorded for any other type of celestial event. Supernovae peak after no more than 70 days, and gravitational lensing events are much shorter. Therefore, this observation defies a simple explanation, said Barbary. “We have never seen anything like it.”

Hubble was aimed at a cluster of galaxies 8 billion light-years away in the spring constellation Bootes. But the mystery object could be anywhere in between, even in the halo of our own Milky Way galaxy.

Papers published by other researchers since the event was reported in June 2006, have suggested a bizarre zoo of possibilities: the core collapse and explosion of a carbon rich star, a collision between a white dwarf and an asteroid, or the collision of a white dwarf with a black hole. At the press conference Barbary was asked what the most bizarre explanation of the object was: “Jokingly, someone said it was another civilization turning on their Large Hadron Collider and exploding,” — which got laughs from the audience. “Don’t quote me on that!,” he added.

But Barbary does not believe that any model offered so far fully explains the observations. “I don’t think we really know what the discovery means until we can observe similar objects in the future.”

All-sky surveys for variable phenomena, such as those to be conducted with the planned Large Synoptic Survey Telescope, may ultimately find similar transient events in the universe.

Source: HubbleSite