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UDFy-38135539 is the Hubble Ultra Deep Field (UDF) classification for a galaxy which (as of October 2010) is the most distant object in the universe observed from Earth, and thus the most distant object known to have existed. Its discovery is formally detailed in the 21 October 2010 article "Spectroscopic Confirmation of a Galaxy at Redshift z=8.6" in the journal Nature, authored by an international team of colleagues comprising Matthew Lehnert, Nicole Nesvadba, Mark Swinbank, Jean-Gabriel Cuby, Simon Morris, Benjamin Clement, C. J. Evans, M.N. Bremer and Stephane Basa.
Detection
The galaxy's image was first captured in the Hubble Ultra Deep Field, the most detailed deep space picture ever taken, by the Hubble telescope's recently attached Wide Field Camera 3 (WFC3) in August and September of 2009. The image data was released to the scientific community, which led to the galaxy's detection by the team of Lehnert and colleagues.
The farther that light from a galaxy travels, the more the light is skewed towards longer, redder wavelengths by the intervening expansion of the universe. This phenomenon is known as redshift, and the greater the redshift observed on Earth, the more distant the source of light is. As seen from the Hubble photo, the galaxy could have possibly been an object intrinsically red and relatively close to Earth, and therefore, confirmation using suitably sensitive spectroscopic equipment was needed. This was possible using the European Southern Observatory's SINFONI-equipped Very Large Telescope unit Yepun, located atop Cerro Paranal in Chile's Atacama Desert. The team observed the galaxy for 16 hours, and then analysed their results over 2 months, and published their findings in Nature, in October 2010.
Characteristics
The galaxy, located in the constellation Fornax, appears as a red smudge in the Hubble image, and is "incredibly faint". It is estimated to contain roughly a billion stars, although it is only about 1/10 or possibly smaller than the diameter of our own galaxy, the Milky Way, and has less than about 1% of the mass of the Milky Way's stars. According to Lehnert (of the Observatoire de Paris), it is forming the same number of stars per year as our galaxy, but they are much smaller and less massive, making it "intensely star forming". The team's analysis determined that it has a redshift of 8.55. For comparison, the previous record-holder for most distant object, the gamma-ray burst GRB 090423, has a redshift of 8.2. The galaxy's light photons now observable on Earth were emitted 13 billion years ago, only 600 million years after the Big Bang, when the universe was only 4% of its current age. It has a light travel distance of more than 4 billion parsecs from our planet (over 13 billion light years), and a luminosity distance of 86.9 billion parsecs (about 283 billion light years).
The light now being observed was created during a time when the universe was supposed to be clouded with hydrogen fog and not fully transparent, and the galaxy's own glow alone would not be intense enough to shine through. Scientists therefore suspect that other as-yet-undetected neighboring galaxies helped clear out a bubble of transparent space around it.
Significance
The universe's first stars, blue giants, were born out of the once-ubiquitous hydrogen fog, and burned bright but had short lifespans. Their existence created the first heavy elements, and intense ultraviolet radiation split atoms into protons and electrons, clearing the hydrogen fog and producing plasma still detectable between closely neighboring stars. The period of opaque space between the Big Bang and this event is referred to as the Dark Ages. The era of star birth which followed is known as the reionization epoch, and lasted from somewhere around 150 million to 800 million years after the Big Bang. Astronomers are trying to pin down when and how the Dark Ages ended. The transparent "bubble" which surrounds UDFy-38135539 proves that 600 million years after the Big Bang, stars in galaxies had almost completed the process of hydrogen reionization which resulted in the end of the Dark Ages, by creating the magnetic field that shaped subsequent galaxies and spurred more star formation. UDFy-38135539 reflects this era, when stars were just beginning to emerge from the cosmic fog. Theoretical models and computer simulations suggest the first galaxies could have formed as early as 200 million years after the Big Bang. Small galaxies like UDFy-38135539 changed the atomic composition of the universe during the reionization epoch; Michele Trenti, an astronomer who was not involved in the study but provided commentary published with the report, says that the discovery of the distant galaxy represents a "fundamental leap forward in observational cosmology". The sources of radiation which caused the epoch are still debated, and Lehnert says scientists "would like to know how reionization proceeded". The discovery makes UDFy-38135539 the first known galaxy to have existed fully within the timeline of the reionization epoch, and those involved believe it will help scientists better understand the era. Caltech astronomer Brent Robertson, commenting on the study, stated that the "galaxy happens to reside at a very special time in cosmic history when the properties of gas in the universe were changing rapidly, and therefore this galaxy and others like it may teach us a lot about the early history of the universe". Nesvadba stated that this is the "first time we know for sure that we're looking at one of the galaxies that cleared out the fog which had filled the very early universe". UDFy-38135539's discovery sheds light on the nature of sources which stripped electrons from hydrogen atoms during the reionization epoch. Swinbank also stated that "there must be other fainter, less massive companion galaxies... which helped make the space around it transparent", because "without this help, light... no matter how brilliant, would have been trapped in the hydrogen fog and we would not have been able to detect it".
Future
Scientists hope to find older galaxies; however, closer to the Big Bang, fewer exist and are dimmer on average. They will therefore be increasingly more difficult to find, since they would be very faint with fewer observable stars. Trenti says that new "most distant" record holders will soon be announced, but only incremental distance gains will be realized until NASA's James Webb Space Telescope becomes operational in 2014. The James Webb telescope should be able to detect galaxies more than 13.4 billion light years away, less than 300 million years after the Big Bang. Bremer states that it, and eventually the European Extremely Large Telescope, which will have a mirror five times the diameter of Yepun's, and is tentatively scheduled for completion in 2018, will enable more detailed study of galaxies at such great distances. Lehnert states that this discovery is not "the limit, perhaps not even that close to it". Trenti says redshift 8.6 is likely to be as high as we can reach with the current generation of telescopes, but that with Hubble, "it might be possible to find some galaxies up to redshift 10". Candidates with higher redshifts than UDFy-38135539's have been reported, but not yet confirmed with light spectrum instruments. Astronomers believe they have other candidates of similar distance which they hope to confirm soon.
See also
- GRB 090423 — a gamma ray burst which previously held the record for most distant object
- IOK-1 — previous record holder for the commonly accepted most distant galaxy
References
- ^ Alan Boyle (2010-10-15). "Scientists pinpoint the farthest galaxy". MSNBC. Retrieved 2010-10-21.
- ^ David Derbyshire. "Astronomers find most remote galaxy ever seen... 13 BILLION light years away". DailyMail.co.uk. Retrieved 2010-10-21.
- ^ Matson, John. "Early Bloomer: Faraway Galaxy Pushes Cosmic View Closer to the Dawn of the Universe". Scientific American. doi:10.1111/j.1365-2966.2009.16176.x. Retrieved 2010-10-21.
- ^ "Dim galaxy is most distant object yet found". New Scientist. Retrieved 2010-10-21.
- ^ "Galaxy is most distant object yet". BBC News. Retrieved 2010-10-21.
- Lehnert, M. D.; Nesvadba, N. P. H.; Cuby, J.-G.; Swinbank, A. M.; Morris, S.; Clément, B.; Evans, C. J.; Bremer, M. N.; Basa, S. (2010). "Spectroscopic confirmation of a galaxy at redshift z = 8.6". Nature. 467: 940–942. doi:10.1038/nature09462.
- ^ "Long Ago and Far, Far, Away: The Oldest Thing Ever Seen in the Universe". Fox News. 2010-10-20.
- ^ "Earliest galaxy helped clear Big Bang's fog". USAToday. 2010-10-20.
- "Astronomers Find Oldest Galaxy Yet". ABCNews. 2010-10-20.
- ^ Trenti, Michele (2010). "Astronomy: Galaxy sets distance mark". Nature. 467: 924–925. doi:10.1038/467924a.
- http://www.eso.org/public/archives/releases/sciencepapers/eso1041/eso1041.pdf
- ^ Andrew Fazekas. "Universe's Most Distant Object Spotted". National Geographic. Retrieved 2010-10-21.
- ^ "Oldest Object in Universe Found". Discovery News. Retrieved 2010-10-21.
- "Most distant galaxy identified". Telegraph.co.uk. Retrieved 2010-10-21.