'Dead' Galaxy May Hide Dark Matter Surprise
While measuring the speed of stars whirling around a nearby dwarf galaxy, astronomers have realized that a reservoir of dark matter may be lurking within.
Astronomers grew suspicious of Triangulum II when they tried to measure its mass. Using 6 stars as tracers, they measured their speed around the galaxy's center. Known only to contain around a 1,000 stars, this particular galaxy is a welterweight by cosmic standards, but looks can be decieving. What they found was an amazingly dense galaxy apparently filled with dark matter.
"The total mass I measured was much, much greater than the mass of the total number of stars - implying that there's a ton of densely packed dark matter contributing to the total mass," said astronomer Evan Kirby, of the California Institute of Technology (Caltech) in Pasadena. "The ratio of dark matter to luminous matter is the highest of any galaxy we know. After I had made my measurements, I was just thinking - wow."
Indeed, dark matter is believed to account for the vast majority of matter in the entire universe - approximately 85 percent is thought to be composed of dark matter particles that do not interact with normal matter, except via the gravitational force.
After clocking the speeds of stars inside Triangulum II with the Keck Observatory, located on Hawaii's Mauna Kea, Kirby's team found that to account for their high speed, there had to me more mass that can be explained by adding up all the stars' masses. Even more, they realized that the tiny galaxy possibly possesses the highest concentration of dark matter yet discovered in any galaxy.
So what's going on? One theory is that, for some reason, Triangulum II may be home to a dense cloud of Weakly Interacting Massive particles, or WIMPs. WIMPs are hypothetical particles that carry mass, but do not interact with normal matter. They are ghostly particles that exert a gravitational force and yet cannot be seen (i.e. they do not interact via the electromagnetic force). However, WIMPs do annihilate with one another should they collide, so if Triangulum II is stuffed full of dark matter particles, we should be able to observe an excess of gamma-ray radiation being emitted from the galaxy.
To make things easier, Triangulum II is known as a "dead" galaxy - it lacks star forming regions and is very faint (in fact, the reason why Kirby's team only tracked 6 stars is that only 6 stars are bright enough to be tracked by the Keck telescope). Therefore, the dwarf galaxy shouldn't produce much in the way of high energy radiation, such as gamma-rays. So if we detect gamma-rays, perhpas this would be the "smoking gun" of WIMP annihilation.
However, other measurements appear to show that stars outside of Triangulum II are moving faster than the ones tracked by Kirby's team, a finding that would, if confirmed, contradict this galactic mass estimate. If this is the case, the stellar speed contradiction may be a sign that our galaxy's gravitational field is ripping Triangulum II apart.
"My next steps are to make measurements to confirm that other group's findings," said Kirby. "If it turns out that those outer stars aren't actually moving faster than the inner ones, then the galaxy could be in what's called dynamic equilibrium. That would make it the most excellent candidate for detecting dark matter with gamma rays."
Artistic rendition of the dark matter halo around the Milky Way galaxy, including multiple satellite galaxies.
March 13, 2013, marks 20 years since the W. M. Keck Observatory began taking observations of the cosmos. Located in arguably one of the most extreme and beautiful places on the planet -- atop Mauna Kea, Hawai'i, 13,803 ft (4,207 m) above sea level -- the twin Keck domes have observed everything from asteroids, planets, exoplanets to dying stars, distant galaxies and nebulae. Seen in this photograph, the Keck I and Keck II telescopes dazzle the skies with their adaptive optics lasers -- a system that helps cancel out the turbulence of the Earth's atmosphere, bringing science some of the clearest views attainable by a ground-based observatory.
To celebrate the last two decades of incredible science, Discovery News has assembled some of the most impressive imagery to come from Keck.
Starting very close to home, the Keck II captured this infrared image of asteroid 2005 YU55 as it flew past Earth on Nov. 8, 2011.
Deeper into the solar system, the Keck NIRC2 near-infrared camera captured this beautiful observation of the oddball Uranus on July 11-12, 2004. The planet's north pole is at 4 o'clock.
This is a mosaic false-color image of thermal heat emission from Saturn and its rings on Feb. 4, 2004, captured by the Keck I telescope at 17.65 micron wavelengths.
A nice image of Saturn with Keck I telescope with the near infrared camera (NIRC) on Nov. 6, 1998. This is a composite of images taken in Z and J bands (1.05 and 1.3 microns), with the color scaling adjusted so it looks like Saturn is supposed to look to the naked eye.
This is Saturn's giant moon Titan -- a composite of three infrared bands captured by the Near Infrared Camera-2 on the 10-meter Keck II telescope. It was taken by astronomer Antonin Bouchez on June 7, 2011.
Another multicolored look at Titan -- a near-infrared color composite image taken with the Keck II adaptive optics system. Titan's surface appears red, while haze layers at progressively higher altitudes in the atmosphere appear green and blue.
This image of Neptune and its largest Tritan was captured by Caltech astronomer Mike Brown in September 2011. It shows the wind-whipped clouds, thought to exceed 1,200 miles per hour along the equator.
A color composite image of Jupiter in the near infrared and its moon Io. The callout at right shows a closeup of the two red spots through a filter which looks deep in the cloud layer to see thermal radiation.
HR 8799: Three exoplanets orbiting a young star 140 light years away are captured using Keck Observatory's near-infrared adaptive optics. This was the first direct observation by a ground-based observatory of worlds orbiting another star (2008).
Now to the extremes -- an image of Stephan's Quintet, a small compact group of galaxies.
The Egg Nebula: This Protoplanetary nebula is reflecting light from a dying star that is shedding its outer layers in the final stages of its life.
This is WR 104, a dying star. Known as a Wolf Rayet star, this massive stellar object will end its life in the most dramatic way -- possibly as a gamma-ray burst. The spiral is caused by gases blasting from the star as it orbits with another massive star.
Narrow-field image of the center of the Milky Way. The arrow marks the location of radio source Sge A*, a supermassive black hole at the center of our galaxy.
A high resolution mid-infrared picture taken of the center of our Milky Way reveals details about dust swirling into the black hole that dominates the region.
A false-color image of a spiral galaxy in the constellation Camelopardalis.
A scintillating square-shaped nebula nestled in the vast sea of stars. Combining infrared data from the Hale Telescope at Palomar Observatory and the Keck II telescope, researchers characterized the remarkably symmetrical “Red Square” nebula.
Galaxy cluster Abell 2218 is acting as a powerful lens, magnifying all galaxies lying behind the cluster's core. The lensed galaxies are all stretched along the shear direction, and some of them are multiply imaged.
The central starburst region of the dwarf galaxy IC 10. In this composite color image, near infrared images obtained with the Keck II telescope have been combined with visible-light images taken with NASA’s Hubble Space Telescope.
Keck I (right) and Keck II (left) domes at Mauna Kea.
Keck I and Keck II aim their adaptive optics lasers at the galactic center.