02 May 2012

The Reflection Nova Messier 78 and the Atacama Pathfinder Experiment telescope (APEX)

APEX Telescope in Chile
The Atacama Pathfinder Experiment telescope (APEX) is a 12 meter diameter telescope. Operated by the European Southern Observatory (ESO), the telescope operates at millimeter and sub-millimeter wavelengths which are wavelengths between infrared light and radio waves.

The APEX telescope is situated at the Chajnantor plateau in the Atacama region of Chile. With an elevation of 5100 meters (3.17 miles), it is one of the highest observatory sites on Earth.

APEX is a 12-metre diameter telescope, operating at millimetre and submillimetre wavelengths — between infrared light and radio waves. Submillimetre astronomy opens a window into the cold, dusty and distant Universe, but the faint signals from space are heavily absorbed by water vapour in the Earth's atmosphere. Chajnantor is an ideal location for such a telescope, as the region is one of the driest on the planet and is more than 750 m higher than the observatories on Mauna Kea, and 2400 m higher than the Very Large Telescope (VLT) on Cerro Paranal.

APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. Operation of APEX at Chajnantor is entrusted to ESO. APEX is a pathfinder for the next-generation submillimetre telescope, the Atacama Large Millimeter/submillimeter Array (ALMA), which is being built and operated on the same plateau.

Messier 78

In the constellation of Orion, 1350 light years away, lies the reflection nebula, Messier 78. Reflection nebulas (nebulae) are clouds of dust which reflect the light of a nearby star or stars. Messier 78 is a fine example of a reflection nebula.

The nebula Messier 78 takes centre stage in this image taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, while the stars powering the bright display take a backseat. The brilliant starlight ricochets off dust particles in the nebula, illuminating it with scattered blue light. Igor Chekalin was the overall winner of ESO’s Hidden Treasures 2010 astrophotography competition with his image of this stunning object.
Photo: ESO

In Messier 78's case, the ultraviolet radiation from the stars that illuminate it is not intense enough to ionise the gas to make it glow. The dust particles simply reflect the starlight that falls on them. Despite this, Messier 78 can easily be observed with a small telescope, being one of the brightest reflection nebulae in the sky.

Sifting through dust near Orion's Belt

Photo Credit: ESO/APEX (MPIfR/ESO/OSO)/T. Stanke et al./Igor Chekalin/Digitized Sky Survey
Image: This image of the region surrounding the reflection nebula Messier 78, just to the north of Orion’s belt, shows clouds of cosmic dust threaded through the nebula like a string of pearls. The submillimeter-wavelength observations, made with the Atacama Pathfinder Experiment telescope and shown here in orange, use the heat glow of interstellar dust grains to show astronomers where new stars are being formed. They are overlaid on a view of the region in visible light.

Dust may sound boring and uninteresting — the surface grime that hides the beauty of an object. But this new image of Messier 78 and surroundings, which reveals the submillimetre-wavelength radiation from dust grains in space, shows that dust can be dazzling. Dust is important to astronomers as dense clouds of gas and dust are the birthplaces of new stars.

In the centre of the image is Messier 78, also known as NGC 2068. When seen in visible light, this region is a reflection nebula, meaning that we see the pale blue glow of starlight reflected from clouds of dust. The APEX observations are overlaid on the visible-light image in orange. Sensitive to longer wavelengths, they reveal the gentle glow of dense cold clumps of dust, some of which are even colder than -250ÂșC. In visible light, this dust is dark and obscuring, which is why telescopes such as APEX are so important for studying the dusty clouds in which stars are born.

Video: Messier 78

One filament seen by APEX appears in visible light as a dark lane of dust cutting across Messier 78. This tells us that the dense dust lies in front of the reflection nebula, blocking its bluish light. Another prominent region of glowing dust seen by APEX overlaps with the visible light from Messier 78 at its lower edge. The lack of a corresponding dark dust lane in the visible light image tells us that this dense region of dust must lie behind the reflection nebula.

Observations of the gas in these clouds reveal gas flowing at high velocity out of some of the dense clumps. These outflows are ejected from young stars while the star is still forming from the surrounding cloud. Their presence is therefore evidence that these clumps are actively forming stars.

At the top of the image is another reflection nebula, NGC 2071. While the lower regions in this image contain only low-mass young stars, NGC 2071 contains a more massive young star with an estimated mass five times that of the Sun, located in the brightest peak seen in the APEX observations.

The APEX observations used in this image were led by Thomas Stanke (ESO), Tom Megeath (University of Toledo, USA), and Amy Stutz (Max Planck Institute for Astronomy, Heidelberg, Germany). For more information about this region as seen in visible light, including the recently discovered — and highly variable — McNeil's Nebula, see eso1105.


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