Molecular clouds in the whirlpool galaxy appear to be embedded in fog

In the stellar delivery room
Molecular clouds in a whirlpool: The blueish features show the distribution of hydrogen molecules in M51, the raw material for forming new stars. The background is a colour image of M51 by the Hubble Space Telescope. Superimposed in blue is the CO(1-0) radiation emitted by carbon monoxide (CO) molecules, as measured for the PAWS study using the millimeter telescopes of the Institut de Radioastronomie Millimétrique (IRAM). The CO molecules are used as tracers for molecular hydrogen. Credit: PAWS Team/IRAM/NASA HST/T. A. Rector, University of Alaska Anchorage

( —A multi-year study of the Whirlpool galaxy (M51) has changed our understanding of giant molecular clouds, in which stars are born. The new study, which mapped 1,500 such clouds, shows that, instead, they are embedded in a kind of molecular fog, which permeates the whole of the galactic disc. Pressure exerted by this fog is crucial in determining whether or not new stars will form within the clouds. The study, led by Eva Schinnerer from the Max Planck Institute for Astronomy, made extensive use of the millimeter telescopes of IRAM, the Institut de Radioastronomie Millimétrique.

Most of a galaxy's stars are born within giant molecular clouds - accumulations of hydrogen molecules with total masses between a thousand and several million times that of our Sun. As a region within such a cloud collapses under its own gravity, it contracts until pressure and temperature are high enough for nuclear fusion to set in: a new star is born.

Now, a new study challenges astronomers' traditional views about these stellar birthplaces. Study leader Eva Schinnerer (Max Planck Institute for Astronomy) explains: "Over the past four years, we have created the most complete map yet of giant molecular clouds in another similar to our own Milky Way, reconstructing the amounts of hydrogen molecules and correlating them with the presence of new or older stars. The picture that is emerging is quite different from what astronomers thought these clouds should be like." The survey, known as PAWS, targeted the Whirlpool galaxy, also known as M51, at a distance of about 23 million light-years in the constellation Canes Venatici ("Hunting dogs").

Annie Hughes, a post-doctoral researcher at MPIA involved in the study, says: "We used to think of giant as solitary objects, drifting within the surrounding interstellar medium of rarified gas in isolated splendor; the main repository of a galaxy's supply of . But our study shows that 50% of the hydrogen is outside the clouds, in a diffuse, disk-shaped hydrogen fog permeating the galaxy!"

This "fog" of surrounding gas plays an important role in star formation. So does a structural feature characteristic of spiral galaxies: the spiral arms, which slowly move through the galaxy like ripples on a lake, and are somewhat more densely filled with stars and gas than the rest of the galactic disk. Sharon Meidt, another MPIA post-doctoral researcher involved in the study, says: "These clouds are definitely not isolated. On the contrary, interactions between clouds, fog, and overall galactic structure appear to hold the key to whether or not a cloud will form new stars. When the molecular fog moves relative to the galaxy's spiral arms, the pressure it exerts on any clouds within is reduced, in line with a physical law known as Bernoulli's principle. Clouds feeling this reduced pressure are unlikely to form ."

Incidentally, Bernoulli's law is also thought to be responsible for part of the well-known shower-curtain effect: shower curtains blowing inward when one takes a hot shower, another display of reduced pressure.

Jerome Pety of the Institut de Radioastronomie Millimétrique (IRAM), which operates the telescopes used for the new observations, says: "It's good to see our telescopes live up to their full potential. A study that needed such extensive observation time, and required both an interferometer to discern vital details and our 30 m antenna to put those details into a larger context, would not have been possible at any other observatory."

Schinnerer concludes: "So far, the Whirlpool galaxy is one example which we have studied in depth. Next, we need to check that what we have found also applies to other galaxies. For our next steps, we hope to profit from both the extension NOEMA of the compound telescope on the Plateau de Bure and from the newly opened compound telescope ALMA in Chile, which will allow in-depth studies of more distant spiral galaxies."

Explore further

Map of galactic clouds where stars are born takes shape

More information: Schinnerer E., et al., The PdBI Arcsecond Whirlpool Survey (PAWS): A Cloud-Scale/Multi-Wavelength View of the Interstellar Medium in a Grand-Design Spiral Galaxy, Astrophysical Journal, Volume 1, 10 December 2013

Pety, J., et al. The PdBI+30m Arcsecond Whirlpool Survey Reveals a Thick Disk of Diffuse Molecular Gas in the M 51 Galaxy, Astrophysical Journal, Volume 1, 10 December 2013

Hughes, A. et al. Probability Distribution Functions of CO(1-0) Brightness and Integrated Intensity in M 51: the PAWS View, Astrophysical Journal, Volume 1, 10 December 2013

Meidt, S., et al. Gas Kinematics on GMC Scales in M 51 with PAWS: Cloud Stabilization through Dynamical Pressure, Astrophysical Journal, Volume 1, 10 December 2013

Hughes, A., et al. A Comparative Study of Giant Molecular Clouds in M 51, M 33 and the Large Magellanic Cloud, Astrophysical Journal, Volume 1, 10 December 2013

Journal information: Astrophysical Journal

Provided by Max Planck Society
Citation: Molecular clouds in the whirlpool galaxy appear to be embedded in fog (2013, December 12) retrieved 25 August 2019 from
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Dec 12, 2013
So, are they saying that the fog and the molecular clouds do not rotate around with the rest of the galaxy? They seem to be saying that the spiral arms are moving, but the clouds and fog are not. I didn't realize that, if that's the case.

Dec 12, 2013
Again, rediscovering science: D Marmet: http://www.newton...dex.html
In papers published about a decade ago, the author and colleagues predicted the widespread presence of hydrogen in the molecular (H2) form in space (Marmet and Reber 1989; Marmet 1990a,b). Although hydrogen in the atomic form is easily detected through radioastronomy, the molecular form is difficult to detect. We showed that the presence of this missing mass would explain the anomalous rotational motion observed in galaxies, which is otherwise explained by exotic hypotheses, such as swarms of invisible brown or white dwarfs, or weird atomic particles called WIMPs or axions, and "quark nuggets."

Dec 12, 2013
The fog is consistent with Sub-Quantum Kinectics, which predicts a slightly accelerated spontaneous production of new matter in the relative vicinity of matter, such as a galaxy. If the galaxy is shaped in a disk, then so would be the surrounding fog that has been forming over billions of years in a relatively slow process. Since the matter forms spontaneously from the underlying matrix, which is unlikely to have any relative motion, I would expect that the new matter would also not necessarily have any motion relative to the adjacent galaxy.

Dec 12, 2013
The best things about this kind of article is that it shows the direct benefits of survey data. without the data from these efforts, we would not have a leg to stand on.

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