Recent observations using Hubble Space Telescope (HST) and the Spitzer space telescope of NASA, revealed a view of the farthest galaxy we have ever spotted. This discovery is an incredible example of how advanced telescopes like HST and Spitzer combined with advanced data analysis and modeling techniques in astrophysics can stretch our limits of observing farther and in distant past of our cosmos. Here's a review of this remarkable discovery.
When researchers recently observed one such massive galaxy cluster MAC J1149+2223 (shown in the image above) located near the constellation of Leo, using HST and Spitzer, they spotted a galaxy (position indicated by the box and then magnified in the image above), which has a redshift of about z ≈ 9.6. Distance of a galaxy from us can be estimated from its observed redshift. For this particular galaxy it turns out to be about 13.2 billion light years (about 125 million million billion kms). This means that the light captured by the HST and Spitzer telescope left this galaxy about 13.2 billion years ago, when our Universe was only (!) about 500 million years old. The galaxy is currently named MAC J1149-JD in the research paper about this discovery that appeared in Nature journal this month.
Observations and discoveries like this are not at all as easy as observing some part of the sky using a beginner's telescope and pointing out an object. The images formed by HST and Spitzer are needed to be analyzed using advanced data analysis techniques and our theoretical understanding of cosmology. Thus, such a discovery is a herculean task indeed. Following brief description of the methodology that led astrophysicists to this discovery will tell us what a marvelous job these scientists have accomplished.
The astronomers analyzed images from different regions of the cluster MAC J1149+2223 using HST data, which is in the visible wavelength-range and Spitzer data in the Infrared (IR) wavelengths. As hydrogen is the most abundant element in the Universe, most of the light coming from galaxies is composed of spectrum of hydrogen in the galaxies. Spectrum of hydrogen is very well understood. It is also known that farther an astronomical object is more red the light coming from it appears (redshift). From how much the light coming from the hydrogen in galaxy, MAC J1149-JD, is redshifted (z ≈ 9.6 ± 0.2) the astrophysicists deduced that they've spotted a galaxy 13.2 billion light years* far. This means that the galaxy was formed 490 ± 15 million years after the Big Bang and this makes it the most distant object astronomers have ever seen with high certainty.
The astronomers further studied the distribution of mass in the cluster MAC J1149+2223. This is very important, as the lensing properties of different regions in the cluster depend on the distribution of mass in that region. The gravitational lensing by different parts of the cluster was observed; images of different objects far 'behind' the cluster were analyzed. The phenomenon of gravitational lensing is well understood theoretically. When the images from MAC J1149+2223 were combined with theoretical models of gravitational lensing, it was estimated that the image of the galaxy that is spotted is about 15 times magnified as compared to the original size of the galaxy, by the gravitational lensing due to the cluster MAC J1149+2223.
From the estimation of the magnification factor it is possible to estimate the size and the mass of the galaxy, the rate of star formation in the galaxy and also how long after the Big Bang most of the stars in the galaxy were formed (star formation age of the galaxy). The mass of MAC J1149-JD was estimated to be about 1.5 x 108 times the mass of our Sun! Based on the observations of the galaxy it is calculated that 13.2 billion years ago, on an average, about 1.2 stars of the size of our Sun were formed in this galaxy every year! All these calculations are based on theoretical models of galaxy formation and star formation in a galaxy. Since these are very first observations of this galaxy not a lot of observational data is available. This adds statistical uncertainty in the observations. In an indirect calculation of any property of the galaxy this uncertainty propagates and usually grows (that's why the word 'about' in this paragraph is typed in italics for emphasis). As a result of such a propagation of uncertainty astrophysicists have not been able to accurately estimate the star formation age of the galaxy. More data is needed to perform such accurate calculations and to reduce the uncertainties in the quantities depicted above. Although, with 95% Confidence Level astrophysicists have calculated the star formation age of MAC J1149-JD to be less than 200 million years.
With more observational data from this galaxy and other such galaxies formed very early in the Universe astronomers can study the processes that led to the formation of different cosmic objects in the early Universe. Such studies can improve our understanding of the Universe we live in. With future advanced telescopes like NASA's James Webb Telescope, planned for launch in 2018, we'll certainly be better equipped to understand our Universe on the cosmic frontier.
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| Image credit: NASA/ESA/STScl/JHU. Original Image |
Our Universe is known to be 13.7 billion years old. Since the Universe is expanding, the galaxies formed very early after the Big Bang are too far away and hence too faint to observe even with most advanced telescopes of today. Think of our day-to-day experience of how we try to observe details of tiny things.... using lenses. On the cosmic level there exist such a phenomenon called the Gravitational Lensing (check the video below), which is like a cosmic lensing effect. Gravitational field near a massive astrophysical object, e.g. a star, a galaxy, a cluster of galaxies, etc., gets so strong that it can bend path of light passing near it significantly. Light coming from a very far away galaxy passing near massive cluster of relatively closer galaxies can bent that light before it reaches us. Effectively this lensing effect can magnify the object farther away, make it look brighter. This can enable us to see galaxies, which are so far away that without the 'lensing' our telescopes are incapable of observing those.
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Video credit: NASA, ESA & L. Carçada. Original video
When researchers recently observed one such massive galaxy cluster MAC J1149+2223 (shown in the image above) located near the constellation of Leo, using HST and Spitzer, they spotted a galaxy (position indicated by the box and then magnified in the image above), which has a redshift of about z ≈ 9.6. Distance of a galaxy from us can be estimated from its observed redshift. For this particular galaxy it turns out to be about 13.2 billion light years (about 125 million million billion kms). This means that the light captured by the HST and Spitzer telescope left this galaxy about 13.2 billion years ago, when our Universe was only (!) about 500 million years old. The galaxy is currently named MAC J1149-JD in the research paper about this discovery that appeared in Nature journal this month.
Observations and discoveries like this are not at all as easy as observing some part of the sky using a beginner's telescope and pointing out an object. The images formed by HST and Spitzer are needed to be analyzed using advanced data analysis techniques and our theoretical understanding of cosmology. Thus, such a discovery is a herculean task indeed. Following brief description of the methodology that led astrophysicists to this discovery will tell us what a marvelous job these scientists have accomplished.
The astronomers analyzed images from different regions of the cluster MAC J1149+2223 using HST data, which is in the visible wavelength-range and Spitzer data in the Infrared (IR) wavelengths. As hydrogen is the most abundant element in the Universe, most of the light coming from galaxies is composed of spectrum of hydrogen in the galaxies. Spectrum of hydrogen is very well understood. It is also known that farther an astronomical object is more red the light coming from it appears (redshift). From how much the light coming from the hydrogen in galaxy, MAC J1149-JD, is redshifted (z ≈ 9.6 ± 0.2) the astrophysicists deduced that they've spotted a galaxy 13.2 billion light years* far. This means that the galaxy was formed 490 ± 15 million years after the Big Bang and this makes it the most distant object astronomers have ever seen with high certainty.
The astronomers further studied the distribution of mass in the cluster MAC J1149+2223. This is very important, as the lensing properties of different regions in the cluster depend on the distribution of mass in that region. The gravitational lensing by different parts of the cluster was observed; images of different objects far 'behind' the cluster were analyzed. The phenomenon of gravitational lensing is well understood theoretically. When the images from MAC J1149+2223 were combined with theoretical models of gravitational lensing, it was estimated that the image of the galaxy that is spotted is about 15 times magnified as compared to the original size of the galaxy, by the gravitational lensing due to the cluster MAC J1149+2223.
From the estimation of the magnification factor it is possible to estimate the size and the mass of the galaxy, the rate of star formation in the galaxy and also how long after the Big Bang most of the stars in the galaxy were formed (star formation age of the galaxy). The mass of MAC J1149-JD was estimated to be about 1.5 x 108 times the mass of our Sun! Based on the observations of the galaxy it is calculated that 13.2 billion years ago, on an average, about 1.2 stars of the size of our Sun were formed in this galaxy every year! All these calculations are based on theoretical models of galaxy formation and star formation in a galaxy. Since these are very first observations of this galaxy not a lot of observational data is available. This adds statistical uncertainty in the observations. In an indirect calculation of any property of the galaxy this uncertainty propagates and usually grows (that's why the word 'about' in this paragraph is typed in italics for emphasis). As a result of such a propagation of uncertainty astrophysicists have not been able to accurately estimate the star formation age of the galaxy. More data is needed to perform such accurate calculations and to reduce the uncertainties in the quantities depicted above. Although, with 95% Confidence Level astrophysicists have calculated the star formation age of MAC J1149-JD to be less than 200 million years.
With more observational data from this galaxy and other such galaxies formed very early in the Universe astronomers can study the processes that led to the formation of different cosmic objects in the early Universe. Such studies can improve our understanding of the Universe we live in. With future advanced telescopes like NASA's James Webb Telescope, planned for launch in 2018, we'll certainly be better equipped to understand our Universe on the cosmic frontier.
* Note: When it is mentioned in literature that a particular astronomical object has been observed, say, 'N' light years away, many people think that that is the distance between us and the object today. I want to clarify that it is not so. When an object is observed 'N' light years away, it means that the light, which we observed left that object 'N' years ago. In other words, the object was at a distance of 'N' light years from us 'N' years ago. This distance is called the 'Proper distance'. Since then the Universe has continued to expand, which means today the object must be farther away from us. This distance is called the 'Comoving distance'. The comoving distance of MAC J1149-JD turns out to be about 32 billion light years from us. That is why I have used the word 'seen' in the title of this post.
Reference:
Wei Zheng, Marc Postman, Adi Zitrin, John Moustakas, Xinwen Shu, Stephanie Jouvel, Ole Høst, Alberto Molino, Larry Bradley, Dan Coe, Leonidas A. Moustakas, Mauricio Carrasco, Holland Ford, Narciso Benítez, Tod R. Lauer, Stella Seitz, Rycha (2012). A magnified young galaxy from about 500 million years after the Big Bang Nature, 489, 406-408 DOI: 10.1038/nature11446
