An image of a galaxy cluster taken by the NASA/ESA Hubble Space Telescope gives a remarkable cross-section of the Universe, showing objects at different distances and stages in cosmic history. They range from cosmic near neighbours to objects seen in the early years of the Universe. The 14-hour exposure shows objects around a billion times fainter than can be seen with the naked eye.
This new Hubble image showcases a remarkable variety of objects at different distances from us, extending back over halfway to the edge of the observable Universe. The galaxies in this image mostly lie within about five billion light-years of us, but the field also contains objects that are both closer and more distant.
Studies of this region of the sky have shown that many of the objects that appear to lie close together may actually be billions of light-years apart. This is because several groups of galaxies lie along our line of sight, creating something of an optical illusion. Hubble’s cross-section of the Universe is completed by distorted images of galaxies in the very distant background.
These objects are sometimes distorted due to a process called gravitational lensing, an extremely valuable technique in astronomy for studying very distant objects [1]. This lensing is caused by the bending of the space-time continuum by massive galaxies lying close to our line of sight to distant objects.
One of the lens systems visible here is called CLASS B1608+656, which appears as a small loop in the centre of the image. It features two foreground galaxies distorting and amplifying the light of a distant quasar. The light from this bright disc of matter, which is currently falling into a black hole, has taken nine billion years to reach us — two thirds of the age of the Universe.
As well as CLASS B1608+656, astronomers have identified two other gravitational lenses within this image. Two galaxies, dubbed Fred and Ginger by the researchers who studied them, contain enough mass to visibly distort the light from objects behind them. Fred, also known more prosaically as [FMK2006] ACS J160919+6532, lies near the lens galaxies in CLASS B1608+656, while Ginger ([FMK2006] ACS J160910+6532) is markedly closer to us. Despite their different distances from us, both can be seen near to CLASS B1608+656 in the central region of this Hubble image.
To capture distant and dim objects like these, Hubble required a long exposure. The image is made up of visible and infrared observations with a total exposure time of 14 hours.
[1] Gravitational lensing can amplify the light coming from distant objects, enabling telescopes like Hubble to see objects that would otherwise be too faint and far away. This effect will be exploited during the Frontier Fieldsobserving campaign in the near future, which aims to combine the power of Hubble with the natural amplification caused by strong gravitational lensing of distant galaxy clusters, to study the past Universe.
Gravitational lensing is an extremely useful phenomenon which allows us as humans (with the help of telescopes) to probe deeper into the universe than ever thought possible. However, due to the refraction of light as light passes through the various interstellar media (such as the variety of gasses including Helium, Hydrogen and newly-discovered diffused polycyclic aromatic hydrocarbons), is it not possible that certain light-emitting sources (planetary bodies in this case) are observed in more than one position during the same exposure? I did research and discovered that although there is refraction to some extent in space, the fact that space is a vacuum means that the amount of refraction is limited and therefore viewing the positions of stars, galaxies and quasars using gravitational lensing does accurately reproduce their positions as observed from Earth.
Every time I read about something like this, they make it sound so simple and easy, but when you actually go and read more about it you realize just how complicated it can get. I didn’t even know that dark matter in the universe plays a huge role in bending light so that we can see galaxies and galaxie clusters.
Even though dark matter is invisible, it does have mass. That is why when light rays coming toward us, will pass through the dark matter’s gravitational field, bending the light called the lensing effect.
Gravitational lensing as mentioned above has helped astronomers figure out the amount of dark matter that is available in the universe and that light bending is the result thereof.
Of course once again technology had the limelight with the Hubble, making all of this possible, helping us to determine the age of the universe and the existence of dark matter.
There’s an atricle on http://www.cfhtlens.org/public/what-gravitational-lensing, explaining it beautifully by Emma Grocutt
[Student number: 04515596] I read an article on http://www.imagine.gsfc.nasa.gov which states that a star, galaxy or quasar that is blocked from our direct view by, for example, another galaxy can be viewed with the use of gravitational lensing – by “bending” or reflecting the light rays around the galaxy to the approximate location of the object that we want to view. How amazing!