التلسكوب هابل يرصد
أبعد المجرات
Eng./Arb
إنكليزي / عربي
Hubble finds farthest galaxies
Oddball galaxies existed following Big Bang
مشاركة :
دانه سعودي
-- كشف العلماء باستخدام
تلسكوب هابل عن صورة قد تكون لأبعد مجرات عن الأرض يتم رصدها حتى الآن.
وتحوي الصورة أجساما غائمة بدرجة تضفي عليها المزيد من الغموض، وقد تتضمن
المجرات القديمة التي تشكلت عقب 700 مليون عام من الانفجار الكبير الذي نشأ
الكون على أثره، ويُطلق على تلك الفترة "الأزمان المظلمة."
ويقول العالم ماسيمو ستيافيلي، من معهد علم تلسكوب الفضاء في بالتيمور، "إن
الصورة هي أعمق رؤية متاحة حتى الآن للكون."
والصورة الجديدة أكثر وضوحا ست مرات من صور سابقة، وأفضل أربع مرات من أبعد صور
كونية التقطها التلسكوب هابل خلال عامي 1995، و1998.
وتتميز الصورة الجديدة بمزيد من الألوان، والكثير من تحولات اللون الأحمر،
الأمر الذي يعود إلى نهايات "الأزمان المظلمة"، عندما تشكلت نجوم أعادت بث
الحرارة في أرجاء الكون الغارق في الظلمة والبرودة وقتذاك، وبدأ الكون يتخلص من
حالة الفوضى العارمة إلى النظام.
وتشير تحولات اللون الأحمر الحادة في الصورة الملتقطة إلى أن المجرات المكتشفة
تقع على مسافة بعيدة، ويعود تاريخها إلى 300 مليون سنة عقب الانفجار الكبير
Eng./Arb
إنكليزي / عربي
. Astronomers using
the Hubble Space Telescope (HST) unveiled the deepest look into the universe
yet, a portrait of what could be the most distant galaxies ever seen.
The new image, called the Hubble Ultra Deep Field (HUDF), includes objects
that until now have been too faint to be seen and includes ancient galaxies
that emerged just 700 million years after the Big Bang theory from what
astronomers call the "Dark Ages" of the universe.
"This image is the deepest view in the visible that we've ever taken, where
an object about as bright as a firefly on the Moon would be visible," said
Massimo Stiavelli, of the Space Telescope Science Institute (STScI) in
Baltimore and the UHDF project leader.
Stiavelli said the new image is six times more sensitive than previous deep
sky surveys and four times better than even Hubble's last faraway looks, the
Hubble Deep Fields (HDFs), taken in 1995 and 1998.
"It has these extra colors with extra red shifts, which leads you to the end
of the Dark Ages, something you couldn't do with the HDF," he added.
The HUDF field contains an estimated 10,000 galaxies in a patch of sky
one-tenth the diameter of the full moon located in the constellation Fornax,
a region just below the constellation Orion. Hubble took one million seconds
to take the HUDF, which appears in an area of the sky that appears largely
empty if observed by ground-based instruments.
This new view is actually two separate images taken by Hubble's Advanced
Camera for Surveys (ACS) and the Near Infrared Camera and Multi-object
Spectrometer (NICMOS). The combination of ACS and NICMOS images will be used
to search for galaxies that existed between 800 and 400 million years after
the Big Bang.
But it's the NICMOS instrument that will reveal the farthest galaxies ever
seen, because only it can detect light stretched past the visible, far into
the near-infrared spectrum. Astronomers can tell how old a galaxy is by
measuring the light it emits, specifically the amount of light that has been
shifted toward the red end of the spectrum.
The higher red shift a galaxy has, the more distant it is and the earlier it
existed in the universe. Hubble researchers are confident their new image
contains galaxies whose light has been stretched to a red shift of 6 or
more.
STScI researchers said there's even a good case that it contains ancient
galaxies of red shift 12, which would place them about 300 million years
after the Big Bang.
Mario Livio, head of the Institute Science Division at Space Telescope
Science Institute, says that if red shift 12 galaxies are indeed in the
image, they will be found soon.
"It could happen this afternoon," Livio said in an interview prior to the
Hubble announcement. "That might be stretching it a bit, but it will be
easy."
Stiavelli, head of ultra deep field observations, said that finding a red
shift 12 galaxy will be important because it will be done not with a
gravitational lens, but "by brute force."
The ACS field is studded with a wide range of galaxies of various sizes,
shapes, and colors. In vibrant contrast to the image's rich harvest of
classic spiral and elliptical galaxies, there is a zoo of oddball galaxies
littering the field. Some look like toothpicks, others like links on a
bracelet. A few galaxies appear to be interacting.
These oddball galaxies, that existed 800 million years after the Big Bang,
chronicle a period when the universe was chaotic, when order and structure
were just beginning to emerge.
"The images will also help us prepare for the next step from NICMOS on
Hubble to the forthcoming James Webb Space Telescope. The NICMOS images
reach back to the distance and time that Webb is destined to explore at much
greater sensitivity," explained Rodger Thompson of the University of Arizona
and the NICMOS principal investigator.
The entire HUDF was observed with the advanced camera's "grism"
spectrograph, an instrument used to measure distances to these distant
objects.
"The grism spectra have already yielded the identification of about a
thousand objects. Included among them are some of the intensely faint and
red points of light in the ACS image, prime candidates for distant
galaxies," said Sangeeta Malhotra of the STScI and Principal Investigator
for the Ultra Deep Field's ACS grism follow-up study.
"Based on those identifications, some of these objects are among the
farthest and youngest galaxies ever seen. The grism spectra also distinguish
among other types of very red objects, such as old and dusty red galaxies,
quasars and cool dwarf stars," she said.
The ACS picture required a series of exposures taken over the course of 400
HST orbits around Earth from September 24, 2003, to January 16, 2004.
The size of a phone booth, ACS captured ancient photons of light that began
traversing the universe even before Earth existed. Photons of light from the
very faintest objects arrived at a trickle of one photon per minute, as
opposed to millions of photons per minute from nearer galaxies.
Astronomers are eager to see the Hubble receive a stay of execution in the
form of future servicing missions by NASA's space shuttles to extend the
telescope's lifetime. Adam Riess, a supernova researcher for STScI, said an
extension could help astronomers find supernova early in the universe's
lifetime.
"There are no supernovae in this deep field, but the results show that
supernova in the early universe could be found if Hubble could be extended,"
Riess said. "Those could provide valuable insight into dark energy and fate
of the universe."
The STScI is operated by the Association of Universities for Research in
Astronomy, Inc. under contract with NASA's Goddard Space Flight Center,
Greenbelt, Maryland. The HST is a project of international cooperation
between NASA and the European Space Agency
The Big Bang theory holds that the universe started with an immense
explosion and that the universe then cooled and became a place of darkness,
lacking stars and galaxies.
About 300 million years after the Big Bang, stars and galaxies began to form
and that would be the limit of the physical universe.
