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Unicorn cloud reveals its inner self

Monoceros R2

Infrared image of the nearby star formation region Monoceros R2, located 2,700 light-years away in the constellation Monoceros (the Unicorn).

  • Infrared images can look through dust clouds
  • VISTA telescope designed for infrared sky surveys
  • Image penetrates into the heart of region called Monoceros R2

A new infrared image from the European Southern Observatory’s (ESO) VISTA survey telescope reveals a scene of glowing tendrils of gas, dark dust clouds and young stars within the constellation Monoceros (the Unicorn).

Known as Monoceros R2, this star-forming region is embedded within a huge dark cloud rich in molecules and dust and hiding an active stellar “nursery”.

VISTA telescope

The enclosure of the VISTA survey telescope at the ESO Paranal Observatory in northern Chile.

At “normal”, visible light wavelengths (see comparison images below), a grouping of massive hot stars can be seen amidst a beautiful collection of “reflection nebulae”, where bluish starlight is scattered from parts of the foggy outer layers of a cloud of molecular gas.

Most of the newborn massive stars in the nursery remain hidden at visible light wavelengths, as the thick dust clouds strongly absorb and block the stars’ ultraviolet and visible light from reaching us.

But spectacular detail pops out at VISTA’s infrared wavelengths. See the full-size, high-resolution version here (0.7MB, new window)

Taken from ESO’s Paranal Observatory in northern Chile, the VISTA image shows how the dark curtain of cosmic dust is penetrated to reveal in detail the folds, loops and filaments sculpted from the dusty interstellar matter by the intense particle winds and radiation emitted by hot young stars.

“When I first saw this image I just said, ‘Wow!’” says Jim Emerson, of Queen Mary, University of London and leader of the VISTA consortium. “I was amazed to see all the dust streamers so clearly around the Monoceros R2 cluster, as well as the jets from highly embedded young stellar objects.”

Stars form in a process that typically lasts few million years and which takes place inside large clouds of interstellar gas and dust, hundreds of light-years across.

Interstellar dust blocks visible light wavelengths but lets infrared and radio wavelengths through… so observations at the latter wavelengths are crucial in the understanding of the earliest stages of the stellar evolution.

Visible light wavelength image of Monoceros R2

A visible light wavelength image of Monoceros R2. Compare this to the infrared image at the top of the page. At infrared wavelengths, the thick, rich dust clouds that cover much of the image become nearly transparent and a whole host of young stars and associated outflows become apparent.

Home to newborn stars

Since dust is largely transparent at infrared wavelengths, many young stars that cannot be seen in visible-light images become apparent in Monoceros R2. The most massive of these stars are less than 10 million years old.

At the centre of the image lies Monoceros R2 dense core, no more than two light-years in extent, which is packed with very massive young stars, as well as a cluster of bright infrared sources, which are typically newborn massive stars still surrounded by dusty clouds.

The rightmost of the bright clouds in the centre is called NGC 2170, the brightest reflection nebula in this region. In visible light, the nebulae appear as bright, light blue islands in a dark ocean, while infrared reveals their interiors where hundreds of massive stars are coming into existence.

NGC 2170—faintly visible through a small telescope—was discovered from England in 1784 by astronomer William Herschel.

Although Monoceros R2 appears close in the sky to the more familiar Orion Nebula it is actually almost twice as far from Earth, at a distance of about 2,700 light-years. The width of VISTA’s field of view is equivalent to about 80 light-years at this distance.

With its 4.1-metre primary mirror, VISTA is the largest survey telescope in the world and is equipped with the largest infrared camera on any telescope, with 67 million pixels. It is dedicated to sky surveys.

By mapping the southern sky systematically, VISTA will gather some 300 gigabytes per night, providing a huge amount of information on those regions that will be studied in greater detail by the Very Large Telescope (VLT), the Atacama Large Millimetre/submillimetre Array (ALMA) and, in the future, by the European Extremely Large Telescope (E-ELT).

Adapted from information issued by ESO / J. Emerson / VISTA / Cambridge Astronomical Survey Unit.

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The Trifid Nebula

The Trifid Nebula

Dark "lanes" of dense interstellar dust trisect the glowing gas of the Trifid Nebula, 9,000 light-years from Earth.

Nine-thousand light-years away in the direction of the constellation Sagittarius, lies the famous Trifid Nebula, so-called for the three dark “lanes” that trisect it.

The Trifid’s triple nature is not limited to the lanes though. It is also three different types of nebulosity in one…it is a reflection, emission and dark nebula in one neat package.

A nebula is a cloud of gas and sometimes dust, floating in interstellar space.

Reflection nebulae have a bluish colour. We see them because light from nearby stars is reflecting off them—the process preferentially reflects the blue wavelengths of the starlight.

Emission nebulae are pinkish. In this case they’re not reflecting light, but emitting their own pale glow. (In the case of the image above, the emission nebulosity looks orange due to the particular wavelength observation used to make the image.)

Silhouetted against brighter backgrounds, dark nebulae stand out like ghostly holes in space. In reality they are very dense clouds of gas and dust particles—they don’t give off or reflect any light to speak of.

The Trifid was discovered in 1764 by the French astronomer Charles Messier, who made it number 20 in his catalogue of “deep sky” objects…hence it’s other common name, M 20.

Messier was a comet hunter who had become frustrated by repeatedly coming across fuzzy blobs in the sky that didn’t turn out to be comets. He decided to make a catalogue of those blobs so that he and other astronomers could learn to ignore them in future.

Ironically, he is now better known for his list of 103 deep sky objects (more were added later by other astronomers) than he is for the 13 comets he discovered.

At the time, Messier thought M 20 was actually a small bunch of stars that couldn’t quite be seen individually. But he did notice the three dark lanes running through it, and gave it the name Trifid.

Story by Jonathan Nally, editor

Image courtesy IAC / Daniel López.

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