Space and Astronomy news daily - SpaceInfo.com.au » Galaxies

Galaxy at the dawn of time

Jonathan Nally — Tue, 03 Jan 2012 13:01:50 +0000

One of the most distant galaxies known, called GN-108036, is seen 750 million years after the Big Bang. The galaxy's light took 12.9 billion years to reach us. Infrared observations taken by NASA's Spitzer and Hubble space telescopes show it to be surprisingly bright, thought to result from an extreme burst of star formation

Galaxy seen as it was 750 million years after the Big Bang
Observations suggest it is forming stars at a furious rate

ASTRONOMERS USING NASA’S Spitzer and Hubble space telescopes have discovered that one of the most distant galaxies known is churning out stars at a shockingly high rate. The blob-shaped galaxy, called GN-108036, is the brightest galaxy found to date at such great distances.

The galaxy, which was discovered and confirmed using ground-based telescopes, is 12.9 billion light-years away.

Data from Spitzer and Hubble were used to measure the galaxy’s high star production rate, equivalent to about 100 Suns per year.

For reference, our Milky Way galaxy is about five times larger and 100 times more massive than GN-108036, but makes roughly 30 times fewer stars per year.

“The discovery is surprising because previous surveys had not found galaxies this bright so early in the history of the universe,” said Mark Dickinson of the US National Optical Astronomy Observatory in Arizona. “Perhaps those surveys were just too small to find galaxies like GN-108036.”

“It may be a special, rare object that we just happened to catch during an extreme burst of star formation.”

Seen shortly after the Big Bang

The international team of astronomers, led by Masami Ouchi of the University of Tokyo, Japan, first identified the remote galaxy after scanning a large patch of sky with the Subaru Telescope atop Mauna Kea in Hawaii.

Its great distance was then carefully confirmed with the W.M. Keck Observatory, also on Mauna Kea.

“We checked our results on three different occasions over two years, and each time confirmed the previous measurement,” said Yoshiaki Ono of the University of Tokyo, lead author of a new paper reporting the findings in the Astrophysical Journal.

The Spitzer (left) and Hubble space telescopes were used to measure the galaxy's redshift, a indication of how far away it is.

GN-108036 lies near the very beginning of time itself, a mere 750 million years after our universe formed 13.7 billion years ago in an explosive “Big Bang.”

Its light has taken 12.9 billion years to reach us, so we are seeing it as it existed in the very distant past.

Remarkable redshift

Astronomers refer to an object’s distance by a number called its “redshift,” which is a measure of how much its light has been stretched to longer, redder wavelengths due to the expansion of the universe.

Objects with larger redshifts are farther away and are seen further back in time.

GN-108036 has a redshift of 7.2. Only a handful of galaxies have confirmed redshifts greater than 7, and only two of these have been reported to be more distant than GN-108036.

Infrared observations from Spitzer and Hubble were crucial for measuring the galaxy’s star-formation activity. Astronomers were surprised to see such a large burst of star formation because the galaxy is so small and from such an early cosmic era.

Back when galaxies were first forming, in the first few hundreds of millions of years after the Big Bang, they were much smaller than they are today, having yet to bulk up in mass.

During this epoch, as the universe expanded and cooled after its explosive start, hydrogen atoms permeating the cosmos formed a thick fog that was opaque to ultraviolet light. This period, before the first stars and galaxies had formed and illuminated the universe, is referred to as the “dark ages.”

The era came to an end when light from the earliest galaxies burned through, or “ionised,” the opaque gas, causing it to become transparent. Galaxies similar to GN-108036 may have played an important role in this event.

Adapted from information issued by NASA / JPL-Caltech / STScI / University of Tokyo.

Get SpaceInfo.com.au daily updates by RSS or email! Click the RSS Feed link at the top right-hand corner of this page, and then save the RSS Feed page to your bookmarks. Or, enter your email address (privacy assured) and we’ll send you daily updates. Or follow us on Twitter, @spaceinfo_oz

Like this story? Please share or recommend it…

Galaxy gazing with The Eyes

Jonathan Nally — Wed, 24 Aug 2011 10:00:30 +0000

A peculiar pair of galaxies, NGC 4438 and NGC 4435, nicknamed The Eyes. The larger of the two, NGC 4438 (top) is thought to have once been a spiral galaxy that was strongly deformed by collisions with other galaxies in the relatively recent past. The two galaxies belong to the Virgo Cluster and are about 50 million light-years away.

The Eyes are two galaxies, NGC 4435 and 4438
Located 50 million light-years from Earth
Probably involved in a collision 100 million years ago

THIS BEAUTIFUL YET PECULIAR pair of galaxies is nicknamed ‘The Eyes’ and is about 50 million light-years from Earth, with the two galaxies some 100,000 light-years apart.

Their nickname comes from the apparent similarity between their cores—two white ovals that resemble a pair of eyes glowing in the dark when seen through a moderate-sized backyard telescope.

But although the centres of these two galaxies look similar, their outskirts could not be more different.

The galaxy in the lower right, known as NGC 4435, is compact and seems to be almost devoid of gas and dust.

In contrast, the large galaxy in the upper left (NGC 4438) has a lane of obscuring dust just below its core, young stars can be seen left of its centre, and gas extends at least up to the edges of the image.

The contents of NGC 4438 have been stripped out by a violent process—a collision with another galaxy that has distorted its spiral shape.

NGC 4435 could be the culprit. Some astronomers think that the damage caused to NGC 4438 resulted from an approach between the two galaxies to within about 16,000 light-years some 100 million years ago.

But while the larger galaxy was damaged, the smaller one was significantly more affected. Gravitational ‘tides’ from the clash are probably responsible for ripping away the contents of NGC 4438, and for removing most of NGC 4435’s gas and dust.

Another possibility is that the giant elliptical galaxy Messier 86, further away from The Eyes and not visible in this image, was responsible for the damage caused to NGC 4438. Recent observations have found filaments of ionised hydrogen gas connecting the two large galaxies, indicating that they may have collided in the past.

Messier 86 and The Eyes belong to the Virgo Cluster, a very rich grouping of galaxies. In such close quarters, galaxy collisions are fairly frequent.

Download wallpapers of The Eyes galaxies (NGC 4438 and NGC 4435):

1024 x 768 (268.4 KB)

1280 x 1024 (510.6 KB)

1600 x 1200 (840.4 KB)

1920 x 1200 (905.5 KB)

Adapted from information issued by ESO / Gems project.

Like this story? Please share or recommend it…

Galaxies are running out of gas

Jonathan Nally — Tue, 23 Aug 2011 03:53:03 +0000

Compared to earlier cosmic epochs, galaxies these days are running of out of the gas raw material with which to make new stars. (Hubble Space Telescope image.)

THE UNIVERSE FORMS FEWER STARS than it used to, and a CSIRO study has now shown why—compared to the past, galaxies today have less gas from which to make stars.

Dr Robert Braun (CSIRO Astronomy and Space Science) and his colleagues used CSIRO’s Mopra radio telescope near Coonabarabran, NSW, to study far-off galaxies and compare them with nearby ones.

Light (and radio waves) from the distant galaxies takes time to travel to us, so we see the galaxies as they were between three and five billion years ago.

Galaxies at that stage of the Universe’s life appear to contain considerably more molecular hydrogen gas than comparable galaxies in today’s Universe, the research team found.

Stars form from clouds of molecular hydrogen. The less molecular hydrogen there is, the fewer stars will form.

The research team’s paper is in press in Monthly Notices of the Royal Astronomical Society.

Raw material for stars

Astronomers have known for at least 15 years that the rate of star formation peaked when the Universe was only a few billion years old and has declined steeply ever since.

“Our result helps us understand why the lights are going out,” Dr Braun said. “Star formation has used up most of the available molecular hydrogen gas.”

CSIRO's Mopra radio telescope near Coonabarabran in New South Wales.

After stars form, they shed gas during various stages of their lives, or in dramatic events such as explosions (supernovae). This returns some gas to space to contribute to further star formation.

“But most of the original gas—about 70%—remains locked up, having been turned into things such as white dwarfs, neutron stars and planets,” Dr Braun said.

“So the molecular gas is used up over time. We find that the decline in the molecular gas is similar to the pattern of decline in star formation, although during the time interval that we have studied, it is declining even more rapidly.”

Dark energy the demon

Ultimately, the real problem is the rate at which galaxies are “refuelled” from outside.

Gas falls into galaxies from the space between galaxies, the intergalactic medium. Two-thirds of the gas in the universe is still found in the intergalactic medium—the space between the galaxies—and only one third has already been consumed by previous star formation in galaxies, astronomers think.

“The drop-off in both gas availability and star formation seems to have started around the time that Dark Energy took control of the Universe,” Dr Braun said.

Up until that time, gravity dominated the Universe, so the gas was naturally pulled in to galaxies, but then the effect of Dark Energy took over and the Universe started expanding faster and faster.

This accelerating expansion has probably made it increasingly difficult for galaxies to capture the additional gas they need to fuel future generations of star formation, Dr Braun speculates.

Adapted from information issued by CSIRO; NASA, ESA, STScI/AURA.

Like this story? Please share or recommend it…

Cosmic expansion rate confirmed

Jonathan Nally — Thu, 28 Jul 2011 07:30:37 +0000

As the universe expands, galaxies move further apart from one another. The rate at which the expansion is proceeding is determined by the Hubble constant, which has been newly measured with high precision.

Hubble constant used to gauge size and age of the universe
Previous measurements had a level of uncertainty
New measurement method confirms earlier results

A STUDENT WITH THE with the International Centre for Radio Astronomy Research (ICRAR) at the University of Western Australia, has calculated how fast the Universe is growing by measuring the Hubble constant.

“The Hubble constant is a key number in astronomy because it’s used to calculate the size and age of the Universe,” said PhD candidate Mr Florian Beutler.

As the Universe expands, it carries other galaxies away from ours. The Hubble constant links how fast the galaxies are moving with how far they are away from us.

By analysing light coming from a distant galaxy, the speed and direction of that galaxy can be easily measured. But determining the galaxy’s distance from Earth is much more difficult.

Until now, this has been done by measuring the brightness of individual objects (such as certain kinds of stars) within a galaxy and using what we know about those objects to calculate how far away the galaxy must be.

This approach is based on some well-established assumptions but is prone to systematic errors, leading Mr Beutler to tackle the problem using a completely different method.

In this plot of 125,000 galaxies from 6df Galaxy Survey data, each dot is a galaxy and Earth is at the centre. (The dark slices are regions blocked from view.) The amount of galaxy clustering has been used (along with other data) to measure the expansion rate of the universe.

New method uses super survey

Published in the Monthly Notices of the Royal Astronomical Society, Mr Beutler’s work draws on data from a survey of more than 125,000 galaxies carried out with the UK Schmidt Telescope in eastern Australia.

Called the 6dF Galaxy Survey, this is the biggest survey of relatively nearby galaxies, covering almost half the sky.

Galaxies are not spread evenly through space, but are clustered. Using a measurement of the clustering of the galaxies surveyed, plus other information derived from observations of the early Universe, Mr Beutler has measured the Hubble constant with an uncertainty of less than 5%.

The new measurement is 67.0 (±3.2) kilometres per second per megaparsec. A megaparsec is 1 million parsecs, or 3.26 million light-years.

Good agreement

“This way of determining the Hubble constant is as direct and precise as other methods, and provides an independent verification of them,” says Professor Matthew Colless, Director of the Australian Astronomical Observatory and one of Mr Beutler’s co-authors.

“The new measurement agrees well with previous ones, and provides a strong check on previous work.”

The measurement can be refined even further by using data from larger galaxy surveys.

“Big surveys, like the one used for this work, generate numerous scientific outcomes for astronomers internationally,” says Professor Lister Staveley-Smith, ICRAR’s Deputy Director of Science.

Adapted from information issued by ICRAR / Images courtesy ICRAR / Chris Fluke, Centre for Astrophysics & Supercomputing, Swinburne University of Technology / NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA.

Like this story? Please share or recommend it…

Fly through a field of galaxies

Jonathan Nally — Tue, 05 Jul 2011 14:01:19 +0000

THIS IMPRESSIVE VIDEO showcases results from a gigantic survey of galaxies known as the 6dF Galaxy Survey. The Survey mapped the nearby universe over almost half the sky, measuring the redshifts of more than 125,000 galaxies. Of those, 11,000 have been specially chosen and have had their velocities measured—their motions through space are helping astronomers to understand the mass involved in each galaxy, and how galaxies move and group together in the wider universe.

The survey gets its name, 6dF, from an innovative instrument installed on the Australian Astronomical Observatory’s UK Schmidt Telescope at Siding Spring in New South Wales. 6dF has a 6-degree-wide field of view—12 times wider than the full Moon—which is very wide for a large telescope. This wide field of view, coupled with the instrument’s ability to study 150 galaxies at a time, makes it an extremely efficient tool with which to do large astronomical survey projects.

The video was produced by Paul Bourke, and was structured so it could be projected on the full dome of a planetarium…which is why it seems to be distorted on a flat screen. Every dot and fuzzy ball you can see is an entire galaxy.

Adapted from information issued by ICRAR / Anglo-Australian Observatory / Paul Bourke (visuals and animation), and Peter Morse and Glenn Rogers (music).

Like this story? Please share or recommend it…

Hubble sees a southern wonder

Jonathan Nally — Wed, 22 Jun 2011 13:59:10 +0000

Resembling looming rain clouds on a stormy day, dark lanes of dust crisscross the heart of the giant elliptical galaxy NGC 5128. Hubble's reveals the vibrant glow of young, blue star clusters and a glimpse into regions normally obscured by the dust.

THE GALAXY KNOWN AS NGC 5128 is a favourite of amateur astronomers in the Southern Hemisphere. Easily visible through a small telescope, it has a rounded shape with a prominent “dark lanes” running through its centre.

Those lanes are composed of interstellar “rivers” of dust encircling the galaxy.

Astronomers have now used the Hubble Space Telescope’s Wide Field Camera 3 to zoom in on this region of NGC 5128 in multi-wavelength observations, resulting in the most detailed view ever of this galaxy.

As well as features in the visible spectrum, the composite shows ultraviolet light from young stars, and near-infrared light, which lets us glimpse some of the detail otherwise obscured by the dust.

The dark dust lane that crosses Centaurus A does not show an absence of stars, but rather a relative lack of starlight, as the opaque clouds block the light of background stars from reaching us.

Hubble’s Wide Field Camera 3 has focused on these dusty regions, which span from corner to corner in this image.

It is thought that at some point in the past, NGC 5128 collided and merged with another galaxy. The shockwaves of this event caused hydrogen gas clouds to coalesce and sparked intense areas of star formation, as seen in its outlying regions and in red patches visible in this Hubble close-up.

This wide-field image shows the full extent of galaxy NGC 5128 and its dark, central dust lanes. NGC 5128 is more than 11 million light-years from Earth.

The galaxy’s compact core contains a very active giant black hole. Powerful jets emanating from the vicinity of the black hole are emitting vast amounts of radio and X-ray radiation (although these are invisible here as Hubble’s instruments).

At just over 11 million light-years distant, NGC 5128is relatively nearby in astronomical terms. However, it is not only close, it is also bright. This makes it a very attractive target for amateur astronomers in the Southern Hemisphere, where it is visible. Stargazers can see the galaxy through binoculars, while larger amateur telescopes begin to unveil the distinctive dusty lanes.

Editor’s note: You’ll often see this galaxy called Centaurus A, but this is not strictly correct. Centaurus A is the name given to a region within the galaxy that is emitting large amounts of radio waves. The overall galaxy is called NGC 5128.

Adapted from information issued by NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: R. O’Connell (University of Virginia) and the WFC3 Scientific Oversight Committee. Wide-angle NGC 5128 image courtesy ESO.

Like this story? Please share or recommend it…

Meet the Meathook Galaxy

Jonathan Nally — Wed, 04 May 2011 10:00:09 +0000

This wide view of the Meathook Galaxy shows its bent spiral arms, and glowing pink regions of hydrogen gas where lots of stars have recently formed.

THE MEATHOOK GALAXY, or NGC 2442, has a dramatically lopsided shape. One spiral arm is tightly folded in on itself and played host to a recent supernova (exploding star), while the other, dotted with glowing regions of recent star formation, extends far out from the galaxy’s core or nucleus.

The galaxy’s distorted shape is thought to be the result of the gravitational pull of a passing galaxy at some point in the past, though astronomers so far have not been able to positively identify the culprit.

The broad view, taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla, Chile, very clearly shows the double hook shape that gives the galaxy its nickname. It also captures several other galaxies close to NGC 2442 as well as many more remote galaxies in the background.

A close-up Hubble view of the Meathook Galaxy shows its core as well as the more compact of its two spiral arms.

The close-up image from the NASA/ESA Hubble Space Telescope focuses on the galaxy’s nucleus and the more compact of its two spiral arms. In 1999, a massive star at the end of its life exploded in this arm…a phenomenon known as a supernova.

By comparing older ground-based observations, previous Hubble images made in 2001, and these shots taken in late 2006, astronomers have been able to study in detail what happened to the star in its dying moments. (By the time of this latest Hubble image, the supernova had faded and is not visible.)

Although the Wide Field Imager, being a ground-based instrument, cannot approach the sharpness of images from Hubble in space, it covers a much bigger section of sky in a single exposure. Combining ground- and space-based imagery often gives astronomers deeper insights.

The wide view also highlights the starting point of the life cycle of stars. Dotted across much of the galaxy, and particularly in the longer of the two spiral arms, are patches of pink and red. This colour comes from hydrogen gas in star-forming cloud regions—the powerful radiation of new-born stars ‘excites’ the gas in the clouds, making them glow a bright shade of red.

The near miss with the other galaxy is likely to have been the trigger for this recent burst of star formation. The same tidal forces that deformed the galaxy also disrupted the gas clouds and made them gravitationally collapse in on themselves, leading to the birth of new stars.

Download wallpapers of the Meathook Galaxy:

1024 x 768 (269.6kb)

1280 x 1024 (411.0kb)

1600 x 1200 (552.8kb)

Adapted from information issued by ESO. Images courtesy NASA/ESA and ESO.

Like this story? Please share or recommend it…

The Andromeda apparition

Jonathan Nally — Tue, 26 Apr 2011 14:01:54 +0000

THE ANDROMEDA GALAXY is a huge spiral galaxy about 2.5 million light-years away from Earth, making it the nearest big galaxy to our Milky Way.

Both Andromeda and our Milky Way are moving through space toward each other, and are expected to crash head-on in about 4.5 billion years from now.

The European Space Agency’s fleet of space telescopes has captured views of Andromeda, also known as M31, in different wavelengths. Most of these wavelengths are invisible to the eye and each shows a different aspect of the galaxy’s nature.

Visible light, as seen by optical ground-based telescopes and our eyes, reveals the various stars that shine in the Andromeda Galaxy, yet it is just one small part of the full spectrum of electromagnetic radiation. There are many different wavelengths that are invisible to us but which are revealed by ESA’s orbiting telescopes.

Starting at the long wavelength end, the Planck spacecraft collects microwaves. These show up particles of incredibly cold dust, at just a few tens of degrees above absolute zero. Slightly higher temperature dust is revealed by the shorter, infrared wavelengths observed by the Herschel space telescope. This dust traces locations in the spiral arms of the Andromeda Galaxy where new stars are being born today.

The XMM-Newton telescope detects wavelengths shorter than visible light, collecting ultraviolet and X-rays. These show older stars, many nearing the end of their lives and others that have already exploded, sending shockwaves rolling through space. By monitoring the core of Andromeda since 2002, XMM-Newton has revealed many variable stars, some of which have undergone large stellar detonations known as novae.

Ultraviolet wavelengths also display the light from extremely massive stars. These are young stars that will not live long. They exhaust their nuclear fuel and explode as supernovae typically within a few tens of millions of years after they are born. The ultraviolet light is usually absorbed by dust and re-emitted as infrared, so the areas where ultraviolet light is seen directly correspond to relatively clear, dust-free parts of Andromeda.

By putting all of these observations together, and seeing Andromeda in its many different colours, astronomers are able to follow the life cycle of the stars.

Adapted from information issued by ESA.

Like this story? Please share or recommend it…

The outer limits

Jonathan Nally — Sun, 24 Apr 2011 01:07:37 +0000

Earlier this year, the Hubble Space Telescope spotted what could be the farthest and one of the very earliest galaxies ever seen in the universe so far. This is the deepest infrared image taken of the universe (deeper even than the Hubble Deep Field; see image below). Based on the galaxy's colour, astronomers believe it is a staggering 13.2 billion light-years away.

HOW FAR CAN WE SEE into the cosmos? And what lies beyond what we can see? Will we ever know what exists beyond the ‘edge of space’?

These questions were posed recently by SpaceInfo readers in response to our story on what astronomers will see one trillion years from now.

They’re very interesting questions indeed. The answers require a bit of thought, and especially they require someone who knows what they’re talking about and can provide them in an understandable manner.

Dr Tamara Davis

Introducing Dr Tamara Davis, a cosmologist and Research Fellow in the Physics Department at the University of Queensland. Tamara is involved in some of the most exciting cosmological research going at the moment, and her achievements were recognised a couple of years ago when she was honoured with the 2009 L’Oréal Women in Science Award.

We’re grateful to Tamara for taking the time to give us the following brief explanation of how far we can see, how far we might be able to see in the future, and why there are some things we’ll never see.

Our cosmic Horizons

by Dr Tamara Davis, University of Queensland

SpaceInfo readers have asked about what lies beyond the reach of our view of the cosmos. This is a great question, and I hope the following explanation will help everyone to understand the situation.

There are actually two types of ‘cosmic horizon’. There’s a limit to how far we can see right now, and a different limit to how far we’ll be able to see in the far future.

The limit to how far we can see right now is called our “particle horizon” because it is the distance to the most far-away “particle” (eg. galaxy) that we can currently see.

The particle horizon arises because light has been able to travel only a finite distance since the Big Bang. If we had been around to shine a light from our position at the time of the Big Bang, then the distance that light could have travelled by now is the distance to our particle horizon.

This kind of horizon is getting bigger as time goes on (as light has more time to travel), and we’re continually able to see things further and further away (and further and further back in time).

Practically speaking, we can’t actually see all the way to our theoretical particle horizon because to do so we’d have to see light that was emitted right at the moment of the Big Bang. The universe was so dense back then that light couldn’t travel very far before getting scattered. It was unable to ‘break out’ from the dense cosmic ‘soup’.

In practical terms the most distant thing we can see is what cosmologists call the “last scattering surface”. This was the state of play about 100,000 years after the Big Bang, when the universe’s density dropped to the point that light could break out and travel relatively unimpeded.

These days we perceive that light as a uniform glow of microwave radiation from all directions, known as the cosmic microwave background. Some of the static picked up by old analogue TVs came from this radiation … so, funnily enough, when you saw fuzz on your TV screen you were actually detecting light from our effective particle horizon!

The Hubble Deep Field is one of the iconic images of space, showing us galaxies into the far distant universe. And the further away a galaxy is, the further back in time we're seeing it.

Edge of the great unknown

The other type of horizon, probably more relevant to the discussion in the original article, is our “event horizon”, which is the limit to how far we will be able to see in the infinite future.

If we were to shine a light outwards from our position now, then the distance it can travel in the future is our event horizon.

Now, you might think that, unless the cosmos were to somehow end, a light beam could travel an infinite distance into an infinite future. But in a universe whose rate of expansion is accelerating (like ours) that isn’t true, so there’s a limit to how far we will be able to see, even given infinite time.

This is because there are distant parts of the universe expanding away from us faster than the speed of light… the only way light from galaxies in the most distant reaches of the universe can reach us is if the universe’s expansion slows down.

It’s a bit like a swimmer caught in a rip, trying to swim back to shore…she can’t swim faster than the rip, so she’ll never make it. Unless the rip slows down she hasn’t got a chance.

But our universe is not slowing down, the expansion is actually speeding up, so light from some distant galaxies will forever be out of view.

This limit is called our “event horizon” because it separates events we will be able to see from events we will never be able to see.

The event horizon is actually a more stringent limit than the particle horizon, because not only do you have to ask whether you can see the particle, but also if you can see it for its entire life.

Many galaxies that we can currently see are actually, by now, well beyond our event horizon—because although we can see them as they were in the past, we will never be able to see them as they are today.

Our current event horizon is at a redshift of 1.8…that’s about 5 giga-parsecs away. (A giga-parsec is one billion parsecs, with a parsec being 3.26 light-years.)

You might have seen the Hubble Deep Field (see image above)—one of the ‘deepest,’ most detailed photos of the universe ever taken. The most distant galaxy in that image is beyond a redshift of 6 (more than 8 giga-parsecs away).

That means that a huge number of the galaxies we can see in that image are now actually beyond our event horizon. The Hubble Deep Field shows us a snapshot of them as they were in the past, but we’ll never be able to communicate with them.

More information

For more information about this subject, and for some scientific diagrams of how far we can see in the universe, you can download a fascinating PDF-format article by Tamara from http://www.physics.uq.edu.au/download/tamarad/astro/scienceimages/Spacetime_diagrams.pdf

She’s also written another great article that helps straighten out this wide topic, “Misconceptions about the Big Bang” (Scientific American, March 2005). And for even more information you can visit her website at http://www.physics.uq.edu.au/download/tamarad/astro/index.html

Distant galaxy image courtesy NASA, ESA, Garth Illingworth (UC Santa Cruz), Rychard Bouwens (UC Santa Cruz and Leiden University) and the HUDF09 Team / A. Feild (STScI). HDF image courtesy R. Williams (STScI), the Hubble Deep Field Team and NASA. Tamara Davis image courtesy timothyburgess.net / Science in Public.

Like this story? Please share or recommend it…

Close encounter of the galactic kind

Jonathan Nally — Fri, 22 Apr 2011 13:59:14 +0000

Galaxies NGC 3169 (left) and NGC 3166 (right) are close enough together to feel each other's distorting gravitational influence. The tug-of-war has warped the spiral shape of NGC 3169, and fragmented the dust lanes in NGC 3166.

Galaxies NGC 3169 and 3166 are 70 million light-years from Earth

They’re close enough together to be warped by each other’s gravity

THE GALAXIES IN THIS COSMIC PAIRING, captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, display some curious features, demonstrating that each member of the duo is close enough to feel the distorting gravitational influence of the other.

The gravitational tug-of-war has warped the spiral shape of one galaxy, NGC 3169 (on the left), and fragmented the dust lanes in its companion, NGC 3166.

Meanwhile, a third, smaller galaxy to the lower right, NGC 3165, has a front-row seat to the gravitational twisting and pulling of its bigger neighbours.

This galactic grouping—located about 70 million light-years away in the direction of the constellation Sextans (The Sextant)—was discovered by the English astronomer William Herschel in 1783.

Modern astronomers have gauged the distance between NGC 3169 (left) and NGC 3166 (right) as a mere 50,000 light-years. That’s only about half the width of our Milky Way galaxy.

In such tight quarters, gravity can start to play havoc with galactic structure.

Mostly ‘armless

Spiral galaxies like NGC 3169 and NGC 3166 tend to have orderly swirls of stars and dust pinwheeling about their glowing centres. Close encounters with other big galaxies can jumble this configuration, often serving as a prelude to the merging of the galaxies into one larger galaxy.

So far, the interactions of NGC 3169 and NGC 3166 have just lent a bit of character. NGC 3169’s arms, shining bright with big, young, blue stars, have been teased apart, and lots of luminous gas has been drawn out from the main body.

In NGC 3166’s case, the dust lanes that also usually outline spiral arms are in disarray. The lack of blue colour indicates that NGC 3166 is not forming many new stars.

Galaxy NGC 3169 with supernova SN 2003cg marked.

Spotting a supernova

NGC 3169 has another distinction—the faint yellow dot beaming through a veil of dark dust just to the left of and close to the galaxy’s centre. This flash is the leftover of a supernova detected in 2003 and known accordingly as SN 2003cg. (Note that this supernova does not still shine today—the image was taken back in 2003.)

A supernova of this variety, classified as a Type Ia, is thought to occur when a dense, hot star called a white dwarf—a remnant of medium-sized stars like our Sun—gravitationally sucks gas away from a nearby companion star.

This added fuel will eventually cause the whole star to explode in a runaway nuclear fusion reaction.

The new image presented here of a remarkable galactic dynamic duo is based on data selected by Igor Chekalin for ESO’s Hidden Treasures 2010 astrophotography competition. Chekalin won the first overall prize and this image received the second highest ranking of the nearly 100 contest entries.

Adapted from information issued by ESO / Igor Chekalin.

Like this story? Please share or recommend it…