Less Dark Matter in Young Galaxies?

A new study of six young, star-forming galaxies suggests they’re less influenced by dark matter than expected. But the results may say more about galaxy evolution than about the nature of dark matter.

When Rubin and Ford collected spectra of ionized hydrogen in Andromeda almost half a century ago, they measured the speed of 67 gas clouds as they whirled about the galaxy’s center with far greater precision than ever before. What the astronomers found was at the time quite curious: beyond 15,000 light-years or so from the galaxy’s center, the clouds’ velocities didn’t slow down — the outermost clouds whirled just as fast as those much closer to the center. Either Andromeda Galaxy was in the midst of flying apart (not likely) or there was some additional matter in the galaxy’s outer reaches that we just couldn’t see.

This groundbreaking result, though not the first to suggest the existence of dark matter, encouraged scientists to start taking the matter seriously. And even though physicists still struggle to detect dark matter particles in the lab, astronomers have had enormous success in supporting their existence.

Since Rubin and Ford’s 1970 publication, scientists have found multiple lines of evidence for dark matter, such as the rotations of galaxies within clusters, weak gravitational lensing, and incredibly large-scale computer simulations of the distribution of galaxies in the universe. These observations suggest that galaxies and even galaxy clusters are ensconced in gigantic, massive dark matter halos, which started coming together before the stars began to shine.

That’s why the six galaxies studied by Genzel’s team proved so surprising.

Like Rubin and Ford, Genzel’s team measured the motion of hydrogen gas clouds. Unlike Rubin and Ford, the new measurements showed that toward the edge of six massive, star-forming galaxies, the clouds did slow down. Averaged data from 97 other (fainter) galaxies show the same result.

That’s not to say there isn’t some dark matter there — just not as much as expected. The dark matter cushions these galaxies lounge in appear to be rather threadbare.

Astronomers Map Milky Way in Incredible Detail

Astronomers have mapped atomic neutral hydrogen across the entire sky, creating an unprecedented portrait of our galaxy and some of its nearest neighbors.

Hydrogen is the single most abundant element in the universe. The simple pairing of a proton and electron is so reactive that atomic hydrogen doesn’t occur naturally on Earth — it reacts with itself or other elements to form molecules instead. But in the large, mostly empty space between stars floats a copious amount of neutral atomic hydrogen.

We only know it’s there when the atom’s lone electron very occasionally flips from an “up” state to a “down” state, releasing a single 21-centimeter radio wave. Modern radio telescopes can easily pick up the faint signal, which multiplies thanks to the wealth of hydrogen atoms. What’s hard is to map that signal across the entire sky — and that’s exactly what astronomers have done in unprecedented detail.

Using two of the world’s largest fully steerable radio dishes, the 100-meter Effelsberg dish near Bonn, Germany, and the 64-meter Parkes dish west of Sydney, Australia, astronomers have generated a survey they’ve dubbed HI4PI. Pronounced “hi four pie,” the survey refers to the abbreviation for neutral hydrogen (HI) and the geometrical reference to the whole sky (4PI, or 4π).

Over thousands of hours on the sky, the dishes took more than a million individual observations. Thousands more hours went into processing dozens of terabytes of data, removing radio interference from broadcast stations, military radar, and other Earthbound sources, then stitching everything together into a seamless map of the hydrogen sky.

The resulting image is incredible: the ultrafine detail reveals fine threads and diffuse clouds in the interstellar medium never seen before. And for astronomers studying faraway X-ray or gamma-ray sources, the map will prove essential in cleaning the window to the distant universe.

The map shows not only the amount of hydrogen at each celestial location, but also the motion of hydrogen across the sky: the 21-centimeter radio signal shifts to slightly lower or higher energies as the hydrogen gas moves toward or away from us, respectively. Watch the video below to take a stepwise look through the data, seeing first the most negative velocities (infalling gas, moving toward Earth) and ending with the most positive radial velocities (receding gas from Earth’s perspective).

The Brightest Planets in April’s Night Sky: How to See them (and When)

Mercury – is an evening „star“ setting soon after dusk. On April 1 it reaches its greatest elongation, when it is 19 degrees east of the sun and is almost directly above it at sunset. In mid-twilight (45 minutes after sundown), Mercury is still 10 degrees above the western horizon. Look quick, however, because within 10 days Mercury fades to invisibility as it passes through its crescent phases and slides back toward the sun. Mercury passes through solar (inferior) conjunction on April 20, but remains too dim to see before dawn, even by month’s end.

Venus – shines very low in the dawn.On the morning of April 23, if you look low to the east-southeast about 45 minutes before sunrise you’ll see a waning crescent moon and well to its upper left, Venus will dazzle.

Mars – low and just north of west at dusk, passed from Aries into Taurus on April 12. It’s now readily identified as the only bright object well to the right of Aldebaran.On the evening of April 28, a 9-percent waxing crescent moon sits about 3 degrees to the upper left of Aldebaran and both are positioned well to the left of Mars.

Jupiter – comes to opposition on April 7, rising in the east near sunset and remaining visible all night long.  Around opposition Jupiter is at its closest to the Earth for the year lso brightest and biggest in telescopes.

Saturn – peeks up over the southeast horizon around the middle of the night. By dawn it’s high in the south.On the following morning (April 17), the moon will have shifted its position relative to Saturn, appearing well off to the left of the ringed planet.

Something Big Exploded in a Galaxy Far, Far Away: What Was It?

At 10:49pm Western Australian time on February 2 this year, cosmic gamma rays hit the NASA satellite, Swift, orbiting the Earth.

Within seconds of the detection, an alert was automatically sent to the University of WA’s Zadko Telescope. It swung into robotic action, taking images of the sky location in the constellation Ophiuchus.

What emerged from the blackness, where nothing was seen before, was a rapidly brightening „optical transient,“ which is something visible in the sky for a brief period of time.

The event, named GRB170202, was a very energetic gamma ray burst (GRB). After less than a minute, the gamma rays switched off, and the GRB appeared as a brightening and then fading optical beacon.

The Zadko Telescope recorded the entire evolution of the optical outburst. During its biggest outburst, GRB170202 was equivalent in brightness to millions of stars shining together from the same location.

About 9 hours 42 mins after the GRB, the Very Large Telescope in Chile acquired the spectrum of the light from the optical afterglow.

This enabled a distance to the burst to be measured: about 12 billion light years. The Universe has expanded to four times the size it was then, 12 billion years ago, the time it took the light to reach Earth.

GRB170202 was so far away, even its host galaxy was not visible, just darkness. Because the GRB was a transient, never to be seen again, it is like turning on a light in a dark room (the host galaxy) and trying to record the detail in the room before the light goes out.

A Car-Size Asteroid Just Whipped by Earth

A car-size asteroid was caught on camera just before it approached within 10,100 miles (16,300 km) of Earth today (April 4) — less than one-twentieth the distance from Earth to the moon.

The 12-foot-wide (3.6 meters) celestial visitor, called 2017 GM, whipped by at 11.5 miles per second (18.5 kilometers per second) compared to Earth early this morning. Scientists at the Mount Lemmon Survey in Arizona first spotted the asteroid yesterday, and researchers with Virtual Telescope Project and Tengara Observatories also snapped a photo before its closest approach with an Arizona telescope.

 

The Most Amazing Space Stories of the Week!

April Fools’ comet

A bright-green comet made its closest approach to Earth at 8:30 p.m. EDT Friday night (0030 GMT on April 1). The blazing ball of icy space rock can still be seen with a small telescope or binoculars.

SpaceX’s historic rocket reflight

Elon Musk’s commercial spaceflight company SpaceX successfully launched and landed a used rocket booster for the first time in spaceflight history. The Falcon 9 rocket lifted off from NASA’s historic Launch Complex 39A at the Kennedy Space Center in Florida, and returned to Earth to stick a landing on a drone ship named „Of Course I Still Love You.“

Juno’s fifth Jupiter flyby

NASA’s Juno spacecraft made a close orbital approach to Jupiter on Monday (March 27), skimming 2,700 miles (4,400 kilometers) above the planet’s cloud tops while taking photos and collecting science data.

New record for women in space

NASA astronaut Peggy Whitson, a flight engineer at the International Space Station, took a 7-hour spacewalk on Thursday (March 30) and set a new record for the most cumulative spacewalking time by a female astronaut. Whitson is also the oldest woman to go to space and will become the first woman to command the space station twice on April 9, when her spacewalking partner, Cmdr. Shane Kimbrough, returns to Earth.

Black hole spews out baby stars

Astronomers have found baby stars in jets of material that a black hole is spitting out into space. The finding may explain how large galaxies, which have black holes at their centers, formed spiral, elliptical or other shapes.

The Sun’s Got Waves — Like Earth’s Atmosphere

Most of the time, the sun and the Earth couldn’t be more different: One is a star, the other a planet; the sun is made of plasma and fuses hydrogen to helium, while the Earth is a solid body heated by radioactive decay (and the sun’s rays). But the two bodies’ atmospheres share something in common: A type of wave that undulates through Earth’s skies may have an analogue in the body of the sun, according to a new study.

NASA’s Solar Dynamics Observatory (SDO) and Solar TErrestrial RElations Observatory (STEREO) mission, which included two spacecraft orbiting the sun, spotted a type of wave called a Rossby wave on the sun’s surface. This type of wave occurs in rotating fluids, such as atmospheres and oceans. The findings could help link several phenomena tied to the sun’s magnetic field, such as the source of sunspots, the length of time those spots last and the origin of the 11-year solar-activity cycle.

Rossby waves also occur in Earth’s atmosphere and oceans, and they help to dictate the planet’s weather, researchers said in a statement.