Swarm of Hydrogen Clouds Flying Away from Center of our Galaxy

A team of astronomers has discovered what appears to be a grand exodus of more than 100 hydrogen clouds streaming away from the center of the Milky Way and heading into intergalactic space.

This observation, made with the National Science Foundation’s Green Bank Telescope (GBT), may give astronomers a clearer picture of the so-called Fermi Bubbles, giant balloons of superheated gas billowing out above and below the disk of our galaxy.

hydrogen clouds expanding from center of Milky Way galaxy
Photo Source: S. Brunier; Design & Illustration: P. Vosteen

The results are presented today at the 231st meeting of the American Astronomical Society in Washington, D.C.

“The center of the Milky Way is a special place,” notes Jay Lockman, an astronomer at the Green Bank Observatory in West Virginia. “At its heart is a black hole several million times more massive than the Sun and there are regions of intense star birth and explosive star destruction.”

These energetic processes, perhaps individually or together, have generated a powerful cosmic “wind” that has blown two enormous bubbles above and below the disk of the Milky Way that are filled with gas at tens-of-millions of degrees. This superheated gas, however, shines feebly at radio, X-ray and gamma-ray wavelengths.

The bubbles appear prominently in observations made by NASA’s Fermi Gamma-ray Space Telescope, which is why astronomers refer to them as the Fermi Bubbles.

“One problem that hinders study of this hot cosmic wind is that the gas has such low density that its emission is very faint, so there is no practical way to track its motion,” notes Lockman. “This is where the hydrogen clouds come in.”

Just like a handful of dust thrown into the air can show the motion of wind on Earth, the hydrogen clouds can act as test particles revealing the flow of the hotter, invisible wind from the center of the Milky Way.

Neutral hydrogen gas, the principal component of these clouds, shines brightly at the radio wavelength of 21 centimeters. These hydrogen clouds were first discovered by a team led by Naomi McClure-Griffiths of the Australian National University using a radio telescope array in Australia. However, that survey was confined to a region just a few degrees around the galactic center, so it gave only limited information on the number and extent of these clouds.

New research with the 100-meter GBT greatly extends these observations.

A group led by Lockman, McClure-Griffiths, and Enrico DiTeodoro, who is also with the Australian National University, mapped a much larger area around the galactic center in search of additional hydrogen clouds that might be entrained in the nuclear wind. They found a gigantic swarm of more than 100 high-velocity gas clouds. The properties of these clouds allow the scientists to learn about the shape of the wind-blown region and the enormous energies that are involved.

“The signature of these clouds being blown out of the Milky Way is that their velocities are crazy,” said Lockman. “Gas motions in the Milky Way are usually quite regular and are dominated by the orderly rotation of the Galaxy. In the Fermi Bubbles we see clouds right next to each other on the sky that have velocities differing by as much as 400 kilometers per second.”

According to the researchers, the most likely explanation for these wildly differing velocities is that they’re traveling within a cone of material that is expanding upward and away from the galactic center, so the front portion is coming toward us and the back part is flying away.

By modeling the distribution and velocities of the clouds, the astronomers found that they would fill a cone stretching above and below the galaxy to a distance of at least 5,000 light-years from the center. The clouds have an average speed of about 330 kilometers per second.

Di Teodoro notes: “What is especially puzzling is that we have not yet found the edge of the swarm of clouds. Somewhere above the galactic center, the hydrogen clouds have to dissipate or become ionized. But we have not found that edge yet, so there’s still a lot to learn.”

Mike Holstine
Business Manager, Green Bank Observatory
+1 (304) 456-2011

Paul Vosteen
Media; Education & Public Outreach
Green Bank Observatory

Astronomers peer into the lair of a mysterious source of cosmic radio bursts

Artist concept of fast radio burst. Image Credit: Design: Danielle Futselaar; photo usage: shutterstock.com Green Bank, January 10, 2018 – Using two of the world’s largest radio telescopes, an international team of astronomers have gained new insight into the extreme home of a mysterious source of cosmic radio bursts.  The discovery suggests that the source of the radio emission lies near a massive black hole or within an extremely powerful nebula, and may help shed light on what is causing these strange bursts. The team presented their findings at the American Astronomical Society’s winter meeting (#AAS231) in Washington, D.C.  The results are presented in the journal Nature. (more…)

Eclipse Event at Green Bank Observatory

Image above is similar to what West Virginians will see if they observe the eclipse this August! (Image source: RedOrbit.com) Have you heard?! This summer, you have the chance to experience a spectacular stellar event! On August 21, the star that brings us spring flowers, warm days by the pool, and the northern lights, a.k.a. our Sun, will be eclipsed by the Moon. Want to see it? You’re invited! The Green Bank Observatory in Green Bank, WV is hosting a Great American Eclipse viewing party. Don’t miss out on this rare event. It’s been 26 years since a partial solar eclipse was visible from West Virginia! A solar eclipse occurs when the Moon’s orbit puts the moon directly between the Sun and Earth, casting a shadow on the Earth’s surface. This only happens during the new moon phase, but we don’t see an eclipse every month because the Moon’s orbital path around the Earth is tilted relative to the Earth’s path around the sun. A perfect alignment between Sun, Moon and Earth is needed for an eclipse.
west to east swath of eclipse coverage
Image showing the west to east swath of totality across North America. The circles to the left and right of the central swath indicate the amount of light that will be visible from the Sun during the peak of the eclipse. In other words, it is the maximum amount of occlusion the Moon will provide during the eclipse.
Map Credit: Michael Zeiler at www.GreatAmericanEclipse.com and Fiske Planetarium
The relative positions of the Earth and Moon matter a lot when determining whether the eclipse will be a total or partial eclipse. This eclipse is called the Great American Eclipse because across an entire narrow swath of the country from west to east, the eclipse will be total. West Virginians will be able to see a 90% partial eclipse this August. This means only 10% of the Sun’s light will be visible from behind the Moon! So join us from 11:00 AM until 4:00 PM for a day of food, fun, and education!
  • Hands-on Activities from 11 AM- 12 PM
  • Lunch and Exhibits from 12 PM – 4 PM
  • SAFE Eclipse Viewing through telescopes and projections. Plus live streaming video of the eclipse provided by NASA from 1 PM – 4 PM
Our Great American Eclipse lunch will be “All American” too! For $5.00 you will be able to purchase:
  • Two slices of pizza and a soda
  • Two hotdogs, chips, and a drink*
  • A hamburger, chips, and a drink*
*Cash Only Options. Additional bags of chips and drinks may be purchased for $0.50 and $1.00 respectively while supplies last. Showing up for the event is free so tell your neighbors, pack up the family, and head to 155 Observatory Rd. Green Bank, WV 24944. Important Note: To safely view the eclipse with your eyes you need to use special eclipse glasses.  These are super dark – much darker than sunglasses! So whether you join our eclipse party or plan to be somewhere else on August 21, you can purchase a pair of eclipse glasses for just $2.00 each at our Gift Shop. Eclipse glasses are on sale now, call (304) 456-2150 for details! Learn more about eclipses and specifically about the Great American Eclipse: We would love to know if you’re joining us! Visit our Great American Eclipse event page on Facebook and let us know you’re attending today!