Posted on by Nancy Atkinson

Minimum Mass for Galaxies Provides Insight on Dark Matter

Dwarf galaxies that are within 500,000 light-years from the Milky Way. Credit: UCI

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More news on dark matter this week: By analyzing light from dwarf galaxies that orbit the Milky Way, scientists believe they have discovered the minimum mass for galaxies in the universe – 10 million times the mass of the sun. This mass could be the smallest known “building block” of the mysterious, invisible substance called dark matter. Stars that form within these building blocks clump together and turn into galaxies. Scientists know very little about the microscopic properties of dark matter, even though it accounts for approximately five-sixths of all matter in the universe. “By knowing this minimum galaxy mass, we can better understand how dark matter behaves, which is essential to one day learning how our universe and life as we know it came to be,” said Louis Strigari, lead author of this study from the University of California, Irvine.

Dark matter governs the growth of structure in the universe. Without it, galaxies like our own Milky Way would not exist. Scientists know how dark matter’s gravity attracts normal matter and causes galaxies to form. They also suspect that small galaxies merge over time to create larger galaxies such as our Milky Way.

The smallest known galaxies, called dwarf galaxies, vary greatly in brightness, from 1,000 times the luminosity of the sun to 10 million times the luminosity of the sun. At least 22 of these dwarf galaxies are known to orbit the Milky Way. UCI scientists studied 18 of them using data obtained with the Keck telescope in Hawaii and the Magellan telescope in Chile, with the goal of calculating their masses. By analyzing stars’ light in each galaxy, they determined how fast the stars were moving. Using those speeds, they calculated the mass of each galaxy.

The researchers expected the masses to vary, with the brightest galaxy weighing the most and the faintest galaxy weighing the least. But surprisingly all dwarf galaxies had the same mass – 10 million times the mass of the sun.

Manoj Kaplinghat, a study co-author and physics and astronomy assistant professor at UCI, explains this finding using an analogy in which humans play the role of dark matter.

“Suppose you are an alien flying over Earth and identifying urban areas from the concentration of lights in the night. From the brightness of the lights, you may surmise, for example, that more humans live in Los Angeles than in Mumbai, but this is not the case,” Kaplinghat said. “What we have discovered is more extreme and akin to saying that all metro areas, even those that are barely visible at night to the aliens, have a population of about 10 million.”

Since dwarf galaxies are mostly dark matter – the ratio of dark matter to normal matter is as large as 10,000 to one – the minimum-mass discovery reveals a fundamental property of dark matter.

“We are excited because these galaxies are virtually invisible, yet contain a tremendous amount of dark matter,” said James Bullock, a study co-author and director of UCI’s Center for Cosmology. “This helps us better understand the particle that makes up dark matter, and it teaches us something about how galaxies form in the universe.”

The scientists say clumps of dark matter may exist that contain no stars. The only dark matter clumps they can detect right now are those that are lit by stars.

Scientists hope to learn about dark matter’s microscopic properties when the Large Hadron Collider in Switzerland becomes operational later this year. The device will accelerate two beams of nuclei in a ring in opposite directions and then slam them together to recreate conditions just after the Big Bang. By doing this, scientists hope to create the dark matter particle in the lab for the first time.

Source: University of California, Irvine

Posted on by Nancy Atkinson

Astronomers Locate High Energy Emissions from the Crab Nebula

Crab Nebula. Credit: NASA/ESA

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Scientists studying the Crab Nebula have discovered high energy gamma rays around the rotation-powered pulsar, the neutron star at the center of this enigmatic nebula. Neutron stars accelerate particles to immense energies, typically one hundred times more than the most powerful accelerators on Earth. Scientists have been uncertain exactly how these systems work and where the particles are accelerated. But by using the gamma-ray telescope on the European Space Agency’s INTEGRAL spacecraft orbiting Earth, astronomers have detected polarized gamma-rays emitting from near the pulsar.

The Crab Nebula was created by a supernova explosion which was seen from Earth by early Chinese and Arab astronomers on July 4, 1054. The explosion left behind a pulsar or rotating neutron star with a nebula of radiating particles around it.

The Crab Pulsar. This image combines optical data from Hubble (in red) and X-ray images from Chandra X-ray Observatory (in blue).
The Crab Pulsar. This image combines optical data from Hubble (in red) and X-ray images from Chandra X-ray Observatory (in blue).

The neutron star contains the mass of the Sun squeezed into a volume of about 10 km radius, rotating very fast – about 30 times a second – thereby generating magnetic fields and accelerating particles. But until now, astronomers didn’t know exactly where the particles were accelerated.
Looking into the heart of the pulsar with Integral’s spectrometer (SPI), the researchers made a detailed study of over 600 observations to assess the polarization – or the alignment – of the waves of high-energy radiation originating from the Crab.

They saw that this polarized radiation is aligned with the rotation axis of the pulsar. So they concluded that a significant portion of the electrons generating the high-energy radiation must originate from a highly-organized structure located very close to the pulsar, very likely directly from the jets themselves. The discovery allows the researchers to discard other theories that locate the origin of this radiation further away from the pulsar.

Credits: NASA/CXC/ASU/J. Hester et al.(for the Chandra image); NASA/HST/ASU/J. Hester et al. (for the Hubble image)
Credits: NASA/CXC/ASU/J. Hester et al.(for the Chandra image); NASA/HST/ASU/J. Hester et al. (for the Hubble image)

Professor Tony Dean of the University’s School of Physics and Astronomy, and one of the researchers, commented that the discovery of such alignment – also matching with the polarization observed in the visible band – is truly remarkable. “The findings have clear implications on many aspects of high energy accelerators such as the Crab,” he added.

“The detection of polarized radiation in space is very complicated and rare, as it requires dedicated instrumentation and an in-depth analysis of very complex data”, said Chris Winkler, Integral Project Scientist at ESA.

The paper ‘Polarized gamma-ray emission from the Crab’ is published this week in Science.

More information about the Integral Spacecraft.

Sources: ESA

Posted on by Nancy Atkinson

Space Station Evades Space Debris

ISS. Credit: NASA

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The International Space Station had to perform an evasive maneuver yesterday to dodge space debris from a Russian satellite that disintegrated earlier this year. ESA’s ATV (Automated Transfer Vehicle) was used to perform the avoidance maneuver, the first time it had been used for such a maneuver. A few things about this maneuver are interesting. First, this is the first time in five years that the ISS has had to perform a debris avoidance maneuver. Second, the maneuver was unusual in that was a retrograde maneuver, which slows the ISS and brings it to a lower orbit instead of higher. The last time a retrograde maneuver was performed was eight years ago. Third, according to Jim Oberg at MSNBC, the Russians deny that the satellite has broken up. Fourth, however, the Mission Control Center in Moscow carried out the maneuver.

The maneuver began on August 27 at 18:11 CEST (16:11 UT) and finished 5 minutes 2 seconds later.
In the current ISS configuration the ATV, which is docked to the aft end of the Russian Zvezda Service module at the back of the station, is the only vehicle that can carry out this kind of maneuver. First, the station was turned 180 degrees so that ATV’s aft thrusters were at the front of the ISS with respect to the station’s flight profile.

Once turned, Jules Verne ATV used its rear thrusters produce a speed of 1 m/s to slow the Station down, lowering it about 1.5 kilometers (1 mile). The space station orbits between 320-400 km (200-250 miles) above the Earth’s surface.

Usually maneuvers raise the orbital altitude in order to compensate for the continual drag the station encounters from the upper atmosphere. But Oberg reported that “because the station is now operating near the upper end of its allowable altitude range, any further increase could have exceeded the lifting performance of planned docking missions over the next few months. Hence NASA had to make the unavoidable and wasteful choice to go in the opposite direction.”

The satellite was a Russian Cosmos-2421 naval surveillance satellite, launched in 2006 and designed for electronic eavesdropping to keep track of Western military vessels. According to U.S. tracking data, the satellite disintegrated on March 14 into hundreds of pieces, and later disintegrated further resulting in over 500 tracked objects, one of the largest debris clouds in space history. But Russian officials say the satellite has not broken up, but only quit working. Find more info on this at MSNBC.

Once the debris avoidance maneuver was complete, the ISS was turned back to its original orbital attitude, and control of the ATV was handed back to the ATV Control Center in Europe.

Sources: ESA, MSNBC

Posted on by Nancy Atkinson

Still Mythbusting

Lunar Landing
Apollo 11 Lunar Module on it way to the moon. Credit: NASA

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It seems fitting that today’s NASA “Image of the Day” is this wonderful image of the lunar lander from the Apollo 11 mission, the Eagle, on its way to land on the moon. Really, truthfully, can anyone really believe that a spectacular image like this can be fake? After last night’s “Mythbusters” show about the Apollo Moon Landing Hoax Myth, I’m cautiously hopeful that at least some people who believe(d) in this myth had their eyes opened and minds changed. Alas, there will always be folks out there who for some reason are set on not believing scientists, engineers or the government and won’t subscribe to any type of proof, be it scientific or television-ific. Perhaps the upcoming Lunar Reconnaissance Orbiter mission will be able to take hi-resolution images of one of the Apollo sites.

But in the meantime, enjoy this great image, taken by the Columbia Command and Service Module Pilot for Apollo 11, Michael Collins. Inside the Eagle were Commander Neil A. Armstrong and Lunar Module Pilot Buzz Aldrin. The long rod-like protrusions under the landing pods are lunar surface sensing probes. Upon contact with the lunar surface, the probes sent a signal to the crew to shut down the descent engine. And then Armstrong said, “Houston, Tranquility Base here. The Eagle has landed.”

And that’s the truth.

For more great NASA images, visit the Image of the Day site

Posted on by Nancy Atkinson

Earth’s Atmosphere is Leaking into Space

Artist impression of ions leaking into space. Credit: NASA/ESA

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Oxygen is constantly leaking out of Earth’s atmosphere and into space. Measurements taken by satellites during the 1980s and 1990s showed the escaping ions were traveling faster the higher they were observed. This implied that some sort of acceleration mechanism was involved. Now, new work on data collected by a group of formation-flying satellites called Cluster shows that Earth’s own magnetic field is accelerating the oxygen away. But don’t worry, compared to the Earth’s stock of the life-supporting gas, the amount escaping is negligible. However, in the far future when the Sun begins to heat up in old age, the balance might change and the oxygen escape may become significant.

From data collected from 2001 to 2003, Cluster amassed information about beams of electrically charged oxygen atoms, known as ions, flowing outwards from the polar regions into space. Cluster also measured the strength and direction of the Earth’s magnetic field whenever the beams were present.

Hans Nilsson, Swedish Institute of Space Physics, headed a team of space scientists who analyzed the data. They discovered that the oxygen ions were being accelerated by changes in the direction of the magnetic field. “It is a bit like a sling-shot effect,” says Nilsson.

Having all four Cluster spacecraft was essential to the analysis because it gave astronomers a way to measure the strength and direction of the magnetic field over a wide area. “Cluster allowed us to measure the gradient of the magnetic field and see how it was changing direction with time,” says Nilsson.

Before the space age, scientists believed that Earth’s magnetic field was filled only with particles from the solar wind, the constant sleet of particles that escapes from the Sun. They thought this formed a large cushion that protected the Earth’s atmosphere from direct interaction with the solar wind.

“We are beginning to realize just how many interactions can take place between the solar wind and the atmosphere,” says Nilsson. Energetic particles from the solar wind can be channeled along the magnetic field lines and, when these impact the atmosphere of the Earth, they can produce aurorae. This occurs over the poles of Earth. The same interactions provide the oxygen ions with enough energy to accelerate out of the atmosphere and reach the Earth’s magnetic environment.

The Cluster data were captured over the poles with the satellites flying at an altitude of anywhere between 30,000 and 64,000 kilometers. The data is helping scientists to understand what might happen in the future. “We can only predict these future changes if we understand the mechanisms involved,” says Nilsson.

Source: ESA

Posted on by Nancy Atkinson

Where In The Universe #18

Here’s this week’s “Where In The Universe?” mystery image. The goal of this challenge is to test your skills and visual knowledge of our universe. Guess where this image is from, and give yourself extra points if you can guess which spacecraft is responsible for the image. As always, don’t peek below before you make your guess. Comments on how you did are welcome.

Ready? Proceed…

This is a brand new image from the Cassini spacecraft orbiting the Saturn system, which took this image of the moon Janus. Janus is 179 kilometers, or 111 miles across, and this view shows a perspective 72 degrees north of the moon’s equator. The image was taken with Cassini’s narrow-angle camera on July 14, 2008 using a spectral filter sensitive to wavelengths of infrared light centered at 752 nanometers. The view was acquired at a distance of approximately 259,000 kilometers (161,000 miles) from Janus. image scale is 2 kilometers (5,085 feet) per pixel.

How’d you do?

For more info about the image, click here.

Posted on by Nancy Atkinson

TV Alert: Mythbusters and the Moon Hoax Myth

Mythbusters. Credit: CollectSpace

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On Wednesday August 27th, at 9 p.m. ET/PT in the US, the famed “Mythbusters” on the Discovery Channel will take on one of the biggest myths ever: the belief the Apollo Moon landings were faked. Some folks who lived through the 1960’s never believed the moon landings actually happened, and some how this belief persisted. In 2001 the Fox Channel aired a show “Conspiracy Theory: Did We Land on the Moon?” and the belief grew. But now the Mythbusters take on the HB’s (hoax believers) who say they have scientific evidence the moon landings were faked. Adam and Jamie will fight bad science with their usual good science. The results? We’ll have to wait and see until tonight. But here’s a preview:

I can’t wait!

For more info:
Mythbusters website.
Article on CollectSpace about the show, includes quotes from Phil Plait
Phil Plait’s Review of the show and links to his previous articles about the show
Phil’s debunking of the Fox moon hoax show

Posted on by Nancy Atkinson

Large Hadron Collider Rap Is a Hit

Kate McAlpine at the LHC. Credit: Telegraph

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Puzzled about particle physics? Want to know what the inside of the Large Hadron Collider looks like? Like music, fun and science? Want to know for sure the LHC won’t create a black hole that will swallow the Earth? Find all of the above in a rap song created by Kate McAlpine, 23, who used to work in the press office of CERN, where on September 10, the LHC will be powered up. The song has been a hit on You Tube, and has been downloaded over 400,000 times. Physicists say the science in the song is “spot on” and provides a rhythmic tour of the mysteries of modern physics and the workings of the LHC, while noting that “the things that it discovers will rock you in the head.” Without further ado, here it is:

McAlpine wrote the rap during her 40-minute morning commute to CERN. “Some more academic people are not too happy and they think it kind of cheapens the science and dumbs it down,” she says. “But I think mostly people are excited to have this rap out there. And a lot of people at CERN just think it’s great, so that’s exciting.”

Source: Telegraph UK

Posted on by Nancy Atkinson

Clash of Clusters Separates Dark Matter From Ordinary Matter

Credit: X-ray(NASA/CXC/Stanford/S.Allen); Optical/Lensing(NASA/STScI/UC Santa Barbara/M.Bradac)

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A powerful collision of galaxy clusters captured by NASA’s Hubble Space Telescope and Chandra X-ray Observatory provides evidence for dark matter and insight into its properties. Observations of the cluster known as MACS J0025.4-1222 indicate that a titanic collision has separated dark matter from ordinary matter. The images also provide an independent confirmation of a similar effect detected previously in a region called the Bullet Cluster. Like the Bullet Cluster, this newly studied cluster shows a clear separation between dark and ordinary matter.

MACS J0025 formed after an enormously energetic collision between two large clusters. Using visible-light images from Hubble, the team was able to infer the distribution of the total mass — dark and ordinary matter. Hubble was used to map the dark matter (colored in blue) using a technique known as gravitational lensing. The Chandra data enabled the astronomers to accurately map the position of the ordinary matter, mostly in the form of hot gas, which glows brightly in X-rays (pink).

As the two clusters that formed MACS J0025 (each almost a whopping quadrillion times the mass of the Sun) merged at speeds of millions of miles per hour, the hot gas in the two clusters collided and slowed down, but the dark matter passed right through the smashup. The separation between the material shown in pink and blue therefore provides observational evidence for dark matter and supports the view that dark-matter particles interact with each other only very weakly or not at all, apart from the pull of gravity.

On the Chandra website, there are two animations, one that shows the different views of this cluster viewed by the different observatories, and another depicting how the galaxies may have collided.

Bullet Cluster. Credit: NASA/CXC/CfA/STScI
Bullet Cluster. Credit: NASA/CXC/CfA/STScI

These new results show that the Bullet Cluster is not an anomalous case and helps answers questions about how dark matter interacts with itself.

Sources: HubbleSite, Chandra

Posted on by Nancy Atkinson

A Chilly Sunrise on Mars

Sunrise on Mars. Credit: NASA/JPL/Caltech/U of AZ

Via Twitter, the Phoenix lander said, “I saw this beautiful sunrise yestersol. Bittersweet, as it means an end to midnight sun in the Martian arctic.” At Phoenix’s location above Mars arctic circle, the sun doesn’t set during the peak of summer in the northern hemisphere. If you recall, Phoenix took a montage of images of the non-setting sun last month.

But now, the period of maximum solar energy is past. On Sol 86, or the 86th Martian day after Phoenix landed, the sun set fully behind a slight rise to the north for about a half hour. This red-filter image taken by the lander’s Surface Stereo Imager, shows the sun rising on the morning of sol 90, Aug. 25, 2008, the last day of the Phoenix nominal mission.

Color poster from UnmannedSpaceflight.com
Color poster from UnmannedSpaceflight.com

The image was taken at 51 minutes past midnight local solar time during the slow sunrise that followed a 75 minute “night.” The skylight in the image is light scattered off atmospheric dust particles and ice crystals.

The folks over at Unmanned Spaceflight created a color poster of the sunrise in honor of Phoenix’s 90th sol on Mars:

Download your very own large or medium size poster.

Phoenix will continue working for another month on Mars, through September 30. It seems there’s many people out there hoping for another short mission extension — for as long as the carbon dioxide ice stays away!

Source: Phoenix News