Lenses galore - Hubble finds large sample of very distant galaxies
Thu Jul 24, 2008 at 15:00 UTC
New Hubble Space Telescope observations of six spectacular galaxy clusters acting as gravitational lenses have given significant insights into the early stages of the Universe.
Scientists have found the largest sample of very distant galaxies seen to date: ten promising candidates thought to lie at a distance of 13 billion light-years.
By using the gravitational magnification from six massive lensing galaxy clusters, the NASA/ESA Hubble Space Telescope has provided scientists with the largest sample of very distant galaxies seen to date. Some of the newly found magnified objects are dimmer than the faintest ones seen in the legendary Hubble Ultra Deep Field, which is usually considered the deepest image of the Universe.
By combining both visible and near-infrared observations from Hubble's Advanced Camera for Surveys (ACS) and Near Infrared Camera and Multi-Object Spectrometer (NICMOS), scientists searched for galaxies that are only visible in near-infrared light. They uncovered 10 candidates believed to lie about 13 billion light-years away (a redshift of approximately 7.5), which means that the light gathered was emitted by the stars when the Universe was still very young -- a mere 700 million years old.
"These candidates could well explain one of the big puzzles plaguing astronomy today. We know that the Universe was reionised within the first 5-600 million years after the Big Bang, but we don't know if the ionising energy came from a smaller number of big galaxies or a more plentiful population of tiny", said Johan Richard, from the California Institute of Technology. The relatively high number of redshift 7.5 galaxies claimed in this survey suggests that most of the ionising energy was produced by dim and abundant galaxies rather than large, scarce ones.
"The challenge for astronomers is that galaxies beyond a distance of 13 billion light-years (past a redshift of 7) are exceedingly faint and are only visible in the near-infrared -- just at the limit of what Hubble can observe" explained Jean-Paul Kneib from the Laboratoire d'Astrophysique de Marseille. This new result was only made possible with some cosmic assistance in the form of gravitational lensing that magnified the light from the distant galaxies enough for Hubble to detect them. A firm confirmation of their distance was beyond even the capabilities of the 10-meter Keck telescope and must await powerful future ground-based telescopes.
Credit: NASA, ESA, and Johan Richard (Caltech, USA). Acknowledgement: Davide de Martin & James Long (ESA/Hubble).
High resolution image.
The picture shows Abell 2218, a rich galaxy cluster composed of thousands of individual galaxies. It sits about 2.1 billion light-years from the Earth (redshift 0.17) in the northern constellation of Draco. When used by astronomers as a powerful gravitational lens to magnify distant galaxies, the cluster allows them to peer far into the Universe. However, it not only magnifies the images of hidden galaxies, but also distorts them into long, thin arcs.
Several arcs in the image can be studied in detail thanks to Hubble's sharp vision. Multiple distorted images of the same galaxies can be identified by comparing the shape of the galaxies and their colour. In addition to the giant arcs, many smaller arclets have been identified.
Credit: NASA, ESA, and Johan Richard (Caltech, USA). Acknowledgement: Davide de Martin & James Long (ESA/Hubble).
High resolution image.
Located in the northern celestial hemisphere, Abell 1703 is composed of over one hundred different galaxies that act as a powerful cosmic telescope, or gravitational lens. The gravitational lens produced by the massive galaxy cluster in the foreground (the yellow mostly elliptical galaxies scattered across the image) bends the light rays in a way that can stretch the images and so amplify the brightness of the light rays from more distant galaxies. In the process it distorts their shapes and produces multiple banana-shaped images of the original galaxies. The result is the stunning image seen here -- a view deeper into the Universe than possible with current technology alone. Abell 1703 is located at 3 billion light-years from the Earth (redshift 0.26).
Credit: NASA, ESA, and Johan Richard (Caltech, USA). Acknowledgement: Davide de Martin & James Long (ESA/Hubble).
High resolution image.
ZwCl 1358+62 is located 3.7 billion light-years from Earth (z=0.33) and is made up of at least 150 individual galaxies. This image depicts multiple blue, red and orange arcs scattered across the image, which represent amplified and stretched images of the galaxies behind the cluster's core. The colours displayed by the various lensed galaxies vary according to their distance and galaxy types. The natural gravitational lensing effect in combination with Hubble's potent mirrors provide astronomers with a powerful set of tools to gather information on the nature of distant galaxies and the workings of the "hidden" world around us.
Credit: NASA, ESA, and Johan Richard (Caltech, USA). Acknowledgement: Davide de Martin & James Long (ESA/Hubble).
High resolution image.
Located 2.7 billion light-years from the Earth (redshift 0.23), Abell 2390 is located in the constellation Pegasus. The large arcs seen around the central cluster are distortions of other objects located behind Abell 2390, the light from which is bent and magnified as it passes by the galaxy cluster. When a massive galaxy cluster acts as a lens, like in these new Hubble images, arcs and arclets of light are formed. The images come in different sizes and shapes depending on how distant they are from us and each other and how close the source light passes by the galaxy cluster itself. The extent to which the image is distorted and the number of copies of the background object created depend on the alignment between the galaxy cluster and the distant body.
Credit: NASA, ESA, and Johan Richard (Caltech, USA). Acknowledgement: Davide de Martin & James Long (ESA/Hubble).
High resolution image.
The central picture shows Abell 2218, a rich galaxy cluster composed of thousands of individual galaxies. It sits about 2.1 billion light-years from the Earth (redshift 0.17) in the northern constellation of Draco. When used by astronomers as a powerful gravitational lens to magnify distant galaxies, the cluster allows them to peer far into the Universe. However, it not only magnifies the images of hidden galaxies, but also distorts them into long, thin arcs.
Several arcs in the image can be studied in detail thanks to Hubble’s sharp vision. Multiple distorted images of the same galaxies can be identified by comparing the shape of the galaxies and their colour. In addition to the giant arcs, many smaller arclets have been identified.
The pictures along the right edge show one of the galaxies viewed at approximately redshift 7.5 with the help of the gravitational lens. The galaxy cannot be seen in the top image, which was taken in the visual range by ACS. In the middle image, taken in the near-infrared by ACS, the galaxy becomes barely visible in the circled region. The galaxy finally becomes fully visible in the bottom image, which is taken by NICMOS in the infrared.
The galaxy is visible in the near-infrared region of the electromagnetic spectrum rather than the visible part because during the 13 billion years the light spent travelling to Earth, the Universe has expanded enough to broaden the wavelength from the visible into the near-infrared.
Credit: NASA, ESA, and Johan Richard (Caltech, USA). Acknowledgement: Davide de Martin & James Long (ESA/Hubble).
High resolution image.
This image illustrates a gravitational lensing effect. Imagine the Earth (represented as a blue sphere on the left), a massive body (represented as a yellow sphere near the centre) and a spiral galaxy are aligned. The massive body distorts the spacetime (represented as the yellow grid) and observers on Earth, instead of seeing the spiral galaxy as it is, see the galaxy distorted, as arcs of light. It is like having a "lens" in front of the galaxy.
First observationally confirmed in 1979, gravitational lenses were predicted by Albert Einstein's theory of General Relativity, a theory that allows astronomers to calculate the path of starlight as it moves through curved space-time. According to the theory, the bending of light is brought about by the presence of matter in the Universe, which causes the fabric of space-time to warp and curve.
Gravitational lensing is the result of this warping of spacetime and is mainly detected around very massive galaxy clusters. Due to the gravitational effect of both the cluster's observable matter and hidden dark matter, the light is bent around the cluster. This bending of light allows the clusters in certain places to act as natural gravitational telescopes that give the light of faint and faraway objects a boost.
Where Earth-bound telescopes fail to detect such faint and distant objects due to the blurring introduced by the Earth's atmosphere, a combination of Hubble's location in space and the magnification of the gravitation lenses provides astronomers with a birds-eye view of these elusive objects.
This technique has already been used numerous times by Hubble and has helped astronomers to find and study many of the most distant known galaxies.
| Source: Space Telescope Science Institute | |
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