Swirling electrons in the whirlpool galaxy

LOFAR radio map of the whirlpool galaxy M51 and its neighbourhood at a frequency of 150 MHz. 

The field covers 4 by 2.6 degrees. 

The observations were performed with the Dutch LOFAR high-band antennas. 

The map shows the distribution of hot electrons in M51 and also a large number of background galaxies.

The inlay shows an enlarged view of M51 at 150 MHz (white contour lines) overlayed onto an optical image of M51 from the Digital Sky Survey (DSS). 

Credit: © David Mulcahy et al., Astronomy & Astrophysics

The whirlpool galaxy Messier 51 (M51) is seen from a distance of approximately 30 million light years.

This galaxy appears almost face-on and displays a beautiful system of spiral arms.

A European team of astronomers was able to observe M51 with the International LOFAR Telescope in the frequency range 115-175 MHz, just above the normal commercial FM radio frequency band of 88-108 MHz.

The team obtained the most sensitive image of any galaxy at frequencies below 1 GHz so far.

With LOFAR's high sensitivity, the disk of M51 in the radio regime could be traced much further out than before.

The astronomers detected cosmic electrons and magnetic fields 40,000 light years away from the center of M51.

With LOFAR's high angular resolution, the spiral arms are clearly visible. Magnetic fields and cosmic rays are densest in spiral arms.

Compared to higher radio frequencies, spiral arms appear broader due to the diffusion of cosmic electrons away from the spiral arms where they have been formed.

The view of galaxies in the radio regime is different to their optical appearance. Whereas optical images show predominantly the visible light from stars, the radio waves unravel two constituents of galaxies that are invisible to optical telescopes: electrons, almost as fast as light, and magnetic fields.

Their role for the stability and evolution of galaxies is increasingly under discussion. The electrons are "cosmic ray" particles produced in the shock fronts of giant supernova explosions. Magnetic fields are generated by dynamo processes driven by gas motions.

When the electrons spiral around the magnetic field lines, radio waves are emitted, a process called synchrotron emission. Its intensity increases with the number and energy of the electrons and with magnetic field strength.

For many decades, radio astronomy has been unable to explore low frequencies below 300 MHz because the ionosphere acts as a barrier of low-frequency radio waves (which are completely blocked below about 10 MHz).

Sophisticated methods of data processing and superfast computers are needed to recover the emission.

Due to these technical challenges, spiral galaxies have hardly been studied before at these very low radio frequencies. The only observations were of poor resolution and no details could be made out.

LOFAR Stations in Europe. 

Credit: © ASTRON, The Netherlands

The target of investigation in David Mulcahy's PhD project was the beautiful spiral galaxy Messier 51 at a distance of about 30 million light years which is visible already in a small telescope in the constellation "Canes Venatici", not far away from the famous Big Dipper (in German: "Großer Wagen") in the sky.

"Low-frequency radio waves are important as they carry information about electrons of relatively low energies that are able to propagate further away from their places of origin in the star-forming spiral arms and are able to illuminate the magnetic fields in the outer parts of galaxies", says David Mulcahy.

"We need to know whether magnetic fields are expelled from galaxies and what their strength is out there."

"This beautiful image, coupled with the important scientific result it represents, illustrates the fantastic advances that can be made at low radio frequencies with the LOFAR telescope", continues Anna Scaife from Southampton University, co-author of the paper.

"Unravelling the mysteries of magnetic fields is crucial to understanding how our Universe works."

"For too long, many of the big questions about magnetic fields have simply been untestable and this new era of radio astronomy is very exciting."

The Low Frequency Array (LOFAR), designed and constructed by ASTRON in the Netherlands, is a brand new radio telescope giving access to very low radio frequencies.

LOFAR explores the relatively unexplored frequency range below 240 MHz and consists of a multitude of small and simple antennas without moving parts.

LOFAR consists of 38 stations in the Netherlands, 6 stations in Germany and one station each in the UK, France and Sweden.

The novelty is the online combination of the signals from all stations in a powerful computing cluster located at the University of Groningen (Netherlands).

Observations of M51 with LOFAR below FM radio frequencies (at 30-80 MHz) have already taken place.

"This opens a new window to the Universe where we do not know how galaxies will look like", concludes Rainer Beck, who supervised David Mulcahy's PhD project.

"Maybe we will see how galaxies are magnetically connected to intergalactic space."

"This is a key experiment in preparation for the planned Square Kilometre Array (SKA) that should tell us how cosmic magnetic fields are generated."

More information: The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR, by D.D. Mulcahy, A. Horneffer, R. Beck et al., 2014, Astronomy & Astrophysics, DOI: 10.1051/0004-6361/201424187

NASA Chandra Captures Whirlpool Galaxy Sparkling in X-rays

Image courtesy X-ray: NASA/CXC/Wesleyan Univ./R.Kilgard, et al; Optical: NASA/STScI.

Nearly a million seconds of observing time with NASA's Chandra X-ray Observatory has revealed a spiral galaxy similar to the Milky Way glittering with hundreds of X-ray points of light.

The galaxy is officially named Messier 51 (M51) or NGC 5194, but often goes by its nickname of the "Whirlpool Galaxy."

Like the Milky Way, the Whirlpool is a spiral galaxy with spectacular arms of stars and dust.

M51 is located 30 million light years from Earth, and its face-on orientation to Earth gives us a perspective that we can never get of our own spiral galactic home.

By using Chandra, astronomers can peer into the Whirlpool to uncover things that can only be detected in X-rays.

In this new composite image, Chandra data are shown in purple. Optical data from the Hubble Space Telescope are red, green and blue.

Most of the X-ray sources are X-ray binaries (XRBs). These systems consist of pairs of objects where a compact star, either a neutron star or, more rarely, a black hole, is capturing material from an orbiting companion star.

The infalling material is accelerated by the intense gravitational field of the compact star and heated to millions of degrees, producing a luminous X-ray source.

The Chandra observations reveal that at least ten of the XRBs in M51 are bright enough to contain black holes. In eight of these systems the black holes are likely capturing material from companion stars that are much more massive than the sun.

Because astronomers have been observing M51 for about a decade with Chandra, they have critical information about how X-ray sources containing black holes behave over time.

The black holes with massive stellar companions are consistently bright over the ten years of Chandra observations.

These results suggest that the high-mass stars in these X-ray sources also have strong winds that allow for a steady stream of material to flow onto the black hole.

A difference between the Milky Way and the Whirlpool galaxy is that M51 is in the midst of merging with a smaller companion galaxy seen in the upper left of the image. Scientists think this galactic interaction is triggering waves of star formation.

The most massive of the newly formed stars will race through their evolution in a few million years and collapse to form neutron stars or black holes.

Most of the XRBs containing black holes in M51 are located close to regions where stars are forming, showing their connection to the oncoming galactic collision.

Previous studies of the Whirlpool Galaxy with Chandra revealed just over 100 X-ray sources. The new dataset, equivalent to about 900,000 seconds of Chandra observing time, reveals nearly 500 X-ray sources.

About 400 of these sources are thought to be within M51, with the remaining either being in front of or behind the galaxy itself.

Much of the diffuse, or fuzzy, X-ray emission in M51 comes from gas that has been superheated by supernova explosions of massive stars.

The Whirlpool Galaxy: NGC 5194

The Whirlpool Galaxy is a classic spiral galaxy. At only 30 million light years distant and fully 60 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky. 

This image is a digital combination of a ground-based image from the 0.9-meter telescope at Kitt Peak National Observatory and a space-based image from the Hubble Space Telescope highlighting sharp features normally too red to be seen.

Image Credit: NASA/Hubble

The Whirlpool Galaxy: M51

This image of the Whirlpool by Martin Pugh took the top accolade of Astronomy Photographer of the Year.

We can clearly see the galaxy's spiral arms, as well as its smaller companion galaxy being torn apart by M51's gravity.

(Image: Martin Pugh)

NASA Hubble Telescope: Whirlpool galaxy

Messier 51a, otherwise known as the Whirlpool galaxy, is one of amateur astronomers' most popular objects, because it can be seen easily with binoculars.

The galaxy is around 23 million light years away, located within the constellation Canes Venatici. In this image, the Whirlpool is shown alongside Messier 51b, a dwarf galaxy with which it interacts.

On 31 May, a supernova was seen in M 51a. Observations by the Hubble Space Telescope suggested that it was the explosion of a yellow supergiant star 18 to 24 times the mass of our sun.

(Image: Karelteuwen )

NASA HST Image: Whirlpool Galaxy in infra-red

This NASA image taken by the Hubble Space Telescope shows a dramatic view of the spiral galaxy M51, dubbed the Whirlpool Galaxy.

Seen in near-infrared light, most of the starlight has been removed, revealing the Whirlpool's skeletal dust stSpiral Galaxy M51ructure.

This new image is the sharpest view of the dense dust in M51

NASA Hubble Image: The Whirlpool Galaxy

These images by NASA's Hubble Space Telescope show off two dramatically different face-on views of the spiral galaxy M51, dubbed the Whirlpool Galaxy.

The image at left, taken in visible light, highlights the attributes of a typical spiral galaxy, including graceful, curving arms, pink star-forming regions, and brilliant blue strands of star clusters.

In the image at right, most of the starlight has been removed, revealing the Whirlpool's skeletal dust structure, as seen in near-infrared light. This new image is the sharpest view of the dense dust in M51. The narrow lanes of dust revealed by Hubble reflect the galaxy's moniker, the Whirlpool Galaxy, as if they were swirling toward the galaxy's core.

To map the galaxy's dust structure, researchers collected the galaxy's starlight by combining images taken in visible and near-infrared light. The visible-light image captured only some of the light; the rest was obscured by dust.

The near-infrared view, however, revealed more starlight because near-infrared light penetrates dust. The researchers then subtracted the total amount of starlight from both images to see the galaxy's dust structure.

The red color in the near-infrared image traces the dust, which is punctuated by hundreds of tiny clumps of stars, each about 65 light-years wide. These stars have never been seen before. The star clusters cannot be seen in visible light because dense dust enshrouds them. The image reveals details as small as 35 light-years across.

Astronomers expected to see large dust clouds, ranging from about 100 light-years to more than 300 light-years wide. Instead, most of the dust is tied up in smooth and diffuse dust lanes. An encounter with another galaxy may have prevented giant clouds from forming.

The Whirlpool Galaxy (M51)

The Whirlpool Galaxy (M51) by Ken Mackintosh (UK). Drawn together by gravity, two galaxies interact. Eventually the smaller galaxy will be torn apart or swallowed by the larger one - a process that will take millions of year