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An island of stars in the making

The NGC 1788 nebula

The NGC 1788 nebula, where stars are being born

The delicate nebula NGC 1788, located in a dark and often neglected corner of the constellation Orion, is revealed in a new and finely nuanced image released by the European Space Agency (ESO).

Although this ghostly cloud is rather isolated from Orion’s bright stars, the latter’s powerful winds and light have had a strong impact on the nebula, forging its shape and making it home to a multitude of infant suns.

Stargazers all over the world are familiar with the distinctive profile of the constellation of Orion (the Hunter). Fewer know about the nebula NGC 1788, a subtle, hidden treasure just a few degrees away from the bright stars in Orion’s belt.

NGC 1788 is a reflection nebula, whose gas and dust scatter the light coming from a small cluster of young stars in such a way that the tenuous glow forms a shape reminiscent of a gigantic bat spreading its wings.

Very few of the stars belonging to the nebula are visible in this image, as most of them are obscured by the dusty cocoons surrounding them. The most prominent, named HD 293815, can be distinguished as the bright star in the upper part of the cloud, just above the centre of the image and the pronounced dark lane of dust extending through the nebula.

Birthplace of stars

Although NGC 1788 appears at first glance to be an isolated cloud, observations covering a field beyond the one presented in this image have revealed that bright, massive stars, belonging to the vast stellar groupings in Orion, have played a decisive role in shaping NGC 1788 and stimulating the formation of its stars. They are also responsible for setting the hydrogen gas ablaze in the parts of the nebula facing Orion, leading to the red, almost vertical rim visible in the left half of the image.

Part of the NGC 1788 nebula

The red glow is hydrogen gas being heated by the light of nearby stars.

All the stars in this region are extremely young, with an average age of only a million years, a blink of an eye compared to the Sun’s age of 4.5 billion years.

Analysing them in detail, astronomers have discovered that these “preschool” stars fall naturally into three well separated classes: the slightly older ones, located on the left side of the red rim, the fairly young ones, to its right, making up the small cluster enclosed in the nebula and illuminating it, and eventually the very youngest stars, still deeply embedded in their nascent dusty cocoons, further to the right.

Although none of the youngest stars are visible in this image because of the obscuring dust, dozens of them have been revealed through observations at infrared and millimetre wavelengths of light.

This fine distribution of stars, with the older ones closer to Orion and the younger ones concentrated on the opposite side, suggests that a wave of star formation, generated around the hot and massive stars in Orion, propagated throughout NGC 1788 and beyond.

This image was obtained using the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile.

Adapted from information issued by ESO.

The Square Kilometre Array

In recent days we’ve brought you animated videos of Australia’s new radio telescope system, ASKAP, taking shape in the Western Australian desert.

Although ASKAP will be a fully-fledged radio telescope system in its own right — and one of the best in the world — it is also a “pathfinder” facility being built in the hope that Australia will win the rights to host the much larger Square Kilometre Array (SKA), which will be the world’s largest radio telescope system.

The video above, produced by the Swinburne Centre for Astrophysics and Supercomputing, showcases the SKA and the amazing astronomical research it will perform.

Adapted from information issued by the Swinburne Centre for Astrophysics and Supercomputing.

Hubble confirms the universe is expanding faster

A map showing the expected location of dark matter withing a region of deep space

A map showing the expected location of dark matter withing a region of deep space

A new study led by European scientists presents the most comprehensive analysis of data from the most ambitious survey ever undertaken by the NASA/ESA Hubble Space Telescope.

The researchers have, for the first time ever, used Hubble data to probe the effects of the natural gravitational “weak lenses” in space and characterise the expansion of the Universe.

A group of astronomers, led by Tim Schrabback of the Leiden Observatory, conducted an intensive study of over 446,000 galaxies within the COSMOS field, the result of the largest survey ever conducted with Hubble. In making the COSMOS survey, Hubble photographed 575 slightly overlapping views of the same part of the Universe using the Advanced Camera for Surveys (ACS) onboard Hubble. It took nearly 1,000 hours of observations.

In addition to the Hubble data, researchers used redshift data from ground-based telescopes to assign distances to 194,000 of the galaxies surveyed (out to a redshift of 5).

“The sheer number of galaxies included in this type of analysis is unprecedented, but more important is the wealth of information we could obtain about the invisible structures in the Universe from this exceptional dataset,” says Patrick Simon from Edinburgh University.

An illustration showing how Hubble looks back in time to "map" evolving dark matter

Hubble looks back in time to "map" evolving dark matter by splitting the background galaxy population into discrete epochs of time (like cutting through rock strata). By measuring the redshift of the "lensing" galaxies used to map the dark matter distribution, scientists can put them into different time/distance "slices".

In particular, the astronomers could “weigh” the large-scale matter distribution in space over large distances. To do this, they made use of the fact that this information is encoded in the distorted shapes of distant galaxies, a phenomenon referred to as weak gravitational lensing.

Using complex algorithms, the team led by Schrabback has improved the standard method and obtained galaxy shape measurements to an unprecedented precision. The results of the study will be published in an upcoming issue of Astronomy and Astrophysics.

The meticulousness and scale of this study enables an independent confirmation that the expansion of the Universe is accelerated by an additional, mysterious component named dark energy. A handful of other such independent confirmations exist.

Astronomers compared real observations with two predictions – one for a dark matter-dominated universe, the other one dominated by dark energy.

COSMOS Project Astronomers compared real observations with two simulations – one for a dark matter-dominated universe, the other one dominated by dark energy. The dark energy one is the closest match.

Scientists need to know how the formation of clumps of matter evolved in the history of the Universe to determine how the gravitational force, which holds matter together, and dark energy, which pulls it apart by accelerating the expansion of the Universe, have affected them.

“Dark energy affects our measurements for two reasons. First, when it is present, galaxy clusters grow more slowly, and secondly, it changes the way the Universe expands, leading to more distant — and more efficiently lensed — galaxies. Our analysis is sensitive to both effects,” says co-author Benjamin Joachimi from the University of Bonn.

“Our study also provides an additional confirmation for Einstein’s theory of general relativity, which predicts how the lensing signal depends on redshift,” adds co-investigator Martin Kilbinger from the Institut d’Astrophysique de Paris and the Excellence Cluster Universe.

The large number of galaxies included in this study, along with information on their redshifts is leading to a clearer map of how, exactly, part of the Universe is laid out; it helps us see its galactic inhabitants and how they are distributed.

“With more accurate information about the distances to the galaxies, we can measure the distribution of the matter between them and us more accurately,” notes co-investigator Jan Hartlap from the University of Bonn.

“Before, most of the studies were done in 2D, like taking a chest X-ray. Our study is more like a 3D reconstruction of the skeleton from a CT scan. On top of that, we are able to watch the skeleton of dark matter mature from the Universe’s youth to the present,” comments William High from Harvard University, another co-author.

Image credits: NASA, ESA, J. Hartlap (University of Bonn), P. Simon (University of Bonn) and T. Schrabback (Leiden Observatory)

Perth’s radio astronomy centre

A new astronomy centre, the International Centre for Radio Astronomy Research, has been established in Perth, Australia, to support and boost Australia’s 21st century radio astronomy research efforts.

Australia is currently building ASKAP, the Australian Square Kilometre Array Pathfinder, which will be a network of 36 radio dish antennae. ASKAP will become one of the world’s foremost astronomy observatories, and for some types of research programs, it will be the best in the world.

As the name suggests, ASKAP is intended to be the forerunner to the Square Kilometre Array, a radio telescope system that will be the world’s largest observatory (in terms of geographical spread). Comprising hundreds of antennae spread over thousands of square kilometres, the total area of all the dishes and other antennae combined will add up to one square kilometre, hence the name.

Australia and southern Africa are vying for the rights to host the facility. A decision is expected sometime within the next couple of years.

Video courtesy of ICRAR.

Smallest known star duo confirmed

Artist's impression of the binary star system known as HM Cancri

About 1,600 light-years away, in a binary star system known as HM Cancri, two dense white dwarf stars orbit each other once every 5.4 minutes, based on data from the Keck Observatory. This artist's rendition shows the dance of these dead stars and the resulting gravitational waves (which would actually be invisible).

Astronomers have identified the smallest known binary star system to date. Called HM Cancri, its consists of two dead stars that revolve around each other in 5.4 minutes, by far the shortest known orbital period of any pair of stars.

The team, led by Gijs Roelofs of the Harvard-Smithsonian Center of Astrophysics, used the 10-meter Keck I telescope in Hawaii and its Low Resolution Imaging Spectrograph to study the velocity changes in the spectral lines in the light coming from HM Cancri.

They saw that as the stars orbited each other, the system’s spectral lines shifted periodically from blue to red and back, in accordance with the Doppler effect. With that velocity information, the astronomers were able to confirm the binary’s 5.4-minute period.

“When the first data from the Keck telescope arrived, and our quick analysis showed the periodic shift of the spectral lines, we knew that we had succeeded. More than ten years after its discovery, we finally had deciphered the nature of HM Cancri,” said Arne Rau of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who led the observations at Keck.

Astronomers proposed several years ago that HM Cancri was an interacting binary consisting of two dead stars and that the 5.4 minute period observed was indeed the orbital period.

The team had been trying to make precise velocity measurements to confirm the period since 2005.

X-ray evidence

HM Cancri was discovered in 1999 as a weak X-ray source in data from the German ROSAT satellite. It comprises two white dwarfs, burnt-out cinders of stars that were once similar to the Sun and contain a highly condensed form of helium, carbon and oxygen. In 2001, the X-ray, and also optical, data suggested that the two stars orbited each other in 5.4 minutes.

Another artist's conception of HM Cancri.

Another artist's conception of HM Cancri. One star is feeding the other.

But the information suggested that the binary system was roughly eight times the diameter of the Earth—equivalent to a quarter of the distance between the Earth and the Moon—or smaller. Astronomers were reluctant to accept this physical description without additional evidence. But at a distance of 16,000 light years from Earth, the binary system shines only one millionth as bright as the faintest stars visible to the naked eye, making it very hard to study. To determine with certainty the period of such a system, astronomers needed to use world’s largest telescopes to collect the additional evidence.

“This type of observation is really at the limit of what is currently possible. Not only does one need the biggest telescopes in the world, but they also have to be equipped with the best instruments available,” said team member Paul Groot of the Radboud University Nijmegen in the Netherlands.

As a result of the successful observations with Keck, astronomers now have a new cosmic laboratory to study the evolution of stars as well as general relativity.

“We know the system must have come from two normal stars that somehow spiralled together in two earlier episodes of mass transfer, but the physics of this process is very poorly understood,” said Gijs Nelemans of the Radboud University who was also part of the team.

He added that the system must be one of the most copious emitters of gravitational waves. “We hope to detect these distortions of space-time directly with the future LISA satellite. HM Cancri will now be a cornerstone system for the mission,” he said.

Adapted from information issued by Keck Observatory / NASA / Tod Strohmayer (GSFC) / Dana Berry (Chandra X-Ray Observatory) / Rob Hynes and Paul Groot, Radboud University.