Astronomers claim first 'dark galaxy' find

nature.com
23 February 2005

Astronomers spot invisible galaxy
Discovery supports most recent theories about exotic dark matter
Mark Peplow

A galaxy that is made almost entirely of dark matter has been
discovered. It's the first galaxy found to have no stars at all, but it
fits well with predictions made by astrophysicists about where the
Universe's missing mass should be.

"We've thrown as many tests at it as we can, and it looks like a dark
galaxy," says Robert Minchin from Cardiff University, UK, one of an
international team of astronomers that made the find.

Dark matter betrays its presence by its gravitational pull: without
dark matter to hold them together, rapidly rotating galaxies would
simply fly apart. Scientists estimate that dark matter must be five
times more abundant than normal matter in our Universe. It is likely to
be made of relatively large subatomic particles that rarely interact
with their surroundings, although these particles have never been
identified.

In fact, more than 90% of our particular Galaxy's mass seems to be dark
matter. The normal matter was pulled into stars, planets and dust
clouds, but this doesn't seem to have happened in the dark galaxy.
"What's bizarre is that the galaxy hasn't converted any gas into stars
at all," says Neil Trentham, an astrophysicist from the University of
Cambridge, UK.

The dark galaxy, named VIRGOHI21, is in the Virgo cluster, a large
group of galaxies about 50 million light years away. It has roughly 10%
of the mass of our own Galaxy, the Milky Way, "but it's not uncommonly
small", says Minchin. The discovery will be reported in the
Astrophysics Journal.

Hydrogen shroud

The team's first clue came from the behaviour of the neutral hydrogen
atoms that shroud this dark region of space. The researchers detected
the characteristic radio-frequency signature of these atoms using the
Lovell Telescope at the Jodrell Bank Observatory near Manchester, UK.
They found that the hydrogen was swirling in exactly the same way as it
would swirl around a normal, brightly lit galaxy.

At first, they assumed that they were simply looking at a dim, dwarf
galaxy. But by watching how the hydrogen moved, the researchers were
able to calculate that the mass of the galaxy is relatively large.
However, normal matter packed that close should have ignited some
stars.

"If it were an ordinary galaxy, then it should be quite bright and
would be visible with a good amateur telescope," says Minchin.

He and his colleagues used the powerful Isaac Newton Telescope on La
Palma in Spain's Canary Islands, to look for any scraps of visible
light from the area; they found nothing. The most likely explanation is
that the galaxy is made of dark matter, Minchin says.

Firm find

The inability to find dark galaxies has been a thorn in the side of
theories about how dark matter shapes our Universe, which predict that
there should be even more dark galaxies than visible ones. "The
predictions were robust, but they hadn't been confirmed until now,"
says astrophysicist Ben Moore of the University of Zurich, Switzerland.

Scientists have also speculated that haloes of dark matter might be the
gravitational seeds of galaxies, attracting enough normal matter to
form stars. "Finding this, and other dark galaxies in the future, will
help us to understand how normal galaxies form," says Minchin.

The team now plans to use radio telescopes to hunt for more dark
galaxies, says Minchin: "There could be many, many more of these things
out there."

References
Minchin R. F. et al . Haensel Astrophys. J. (in press), preprint at
http://www.arxiv.org/abs/astro-ph/0502312 (2005).

On Thu, 24 Feb 2005 05:39:19 +0000, MrPepper11 wrote:

nature.com
23 February 2005

Astronomers spot invisible galaxy
Discovery supports most recent theories about exotic dark matter Mark
Peplow

A galaxy that is made almost entirely of dark matter has been
discovered. It's the first galaxy found to have no stars at all, but it
fits well with predictions made by astrophysicists about where the
Universe's missing mass should be.

Why should it be called a "galaxy" and not just a rotating gas cloud or a
rotating cloud of dark matter ?

Dictionaries say a galaxy contains star, gas, dust, etc.

--

Gautam Majumdar

Please send e-mails to

"Gautam Majumdar" wrote in message
. uk...
On Thu, 24 Feb 2005 05:39:19 +0000, MrPepper11 wrote:

nature.com
23 February 2005

Astronomers spot invisible galaxy
Discovery supports most recent theories about exotic dark matter Mark
Peplow

A galaxy that is made almost entirely of dark matter has been
discovered. It's the first galaxy found to have no stars at all, but it
fits well with predictions made by astrophysicists about where the
Universe's missing mass should be.

Why should it be called a "galaxy" and not just a rotating gas cloud or a
rotating cloud of dark matter ?

Dictionaries say a galaxy contains star, gas, dust, etc.


Good point, but maybe it has some faint stars not detectable yet. The INT
is a relatively small telescope, and if the "galaxy" contained only old,
faint stars such as those found in globular clusters, but spread thinly in
space, I'm not sure they could be detected that far away without very
special efforts being made--and maybe not even then. Such stars would be
individually as faint as 30th mag (a quick and rough guess).

A galaxy does not have to contain gas and dust to be so called--most
elliptical galaxies have very little of either, but we still call them
galaxies. But they ought to have at least some stars...

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

John Sefton wrote:


Does a Hydrogen atom without
an electron qualify as an atom?

Atoms are determined by the makeup of their nuclei.
Why did you post your question?

John Sefton wrote:


Mike Dworetsky wrote:

"Gautam Majumdar" wrote in message
. uk...

On Thu, 24 Feb 2005 05:39:19 +0000, MrPepper11 wrote:


nature.com
23 February 2005

Astronomers spot invisible galaxy
Discovery supports most recent theories about exotic dark matter Mark
Peplow

A galaxy that is made almost entirely of dark matter has been
discovered. It's the first galaxy found to have no stars at all, but it
fits well with predictions made by astrophysicists about where the
Universe's missing mass should be.


Why should it be called a "galaxy" and not just a rotating gas cloud
or a
rotating cloud of dark matter ?

Dictionaries say a galaxy contains star, gas, dust, etc.



Good point, but maybe it has some faint stars not detectable yet. The
INT
is a relatively small telescope, and if the "galaxy" contained only old,
faint stars such as those found in globular clusters, but spread
thinly in
space, I'm not sure they could be detected that far away without very
special efforts being made--and maybe not even then. Such stars would be
individually as faint as 30th mag (a quick and rough guess).

A galaxy does not have to contain gas and dust to be so called--most
elliptical galaxies have very little of either, but we still call them
galaxies. But they ought to have at least some stars...


Does a Hydrogen atom without
an electron qualify as an atom?
John


No, an atom is at least a proton and a bound electron. Unbound protons
and electrons and ions are termed a plasma ...

Isn't this a matter of semantics?
Like if a husband says something in a forest with no wife within
earshot, is he still wrong? :-)

John Sefton wrote:

Does a Hydrogen atom without
an electron qualify as an atom?

So... when will we see proof of 'dark energy' mentioned in this
article:

Astronomers detect first invisible galaxy
Breakthrough could shed light on dark-matter mystery
By Robert Roy Britt
Senior science writer, Space.com

Astronomers have discovered an invisible galaxy that could be the
first of many that will help unravel one of the universe's greatest
mysteries.

The object appears to be made mostly of "dark matter," material of an
unknown nature that can't be seen.

Theorists have long said most of the universe is made of dark matter.
Its presence is required to explain the extra gravitational force that
is observed to hold regular galaxies together and that also binds
large clusters of galaxies.

Theorists also believe knots of dark matter were integral to the
formation of the first stars and galaxies. In the early universe, dark
matter condensed like water droplets on a spider web, the thinking
goes. Regular matter - mostly hydrogen gas - was gravitationally
attracted to a dark matter knot, and when the density became great
enough, a star would form, marking the birth of a galaxy.

The theory suggests that pockets of pure dark matter ought to remain
sprinkled across the cosmos. In 2001, a team led by Neil Trentham of
the University of Cambridge predicted the presence of entire dark
galaxies.

One of perhaps many

The newfound dark galaxy was detected with radio telescopes. Similar
objects could be very common or very rare, said Robert Minchin of
Cardiff University in Wales.

"If they are the missing dark matter halos predicted by galaxy
formation simulations but not found in optical surveys, then there
could be more dark galaxies than ordinary ones," Minchin told
Space.com.

In a cluster of galaxies known as Virgo, 50 million light-years away,
Minchin and colleagues looked for radio-wavelength radiation coming
from hydrogen gas. They found a well of it that contains a hundred
million times the mass of the sun. It is now named VIRGOHI21.

The well of material rotates too quickly to be explained by the
observed amount of gas. Something else must serve as gravitational
glue.

"From the speed it is spinning, we realized that VIRGOHI21 was a
thousand times more massive than could be accounted for by the
observed hydrogen atoms alone," Minchin said. "If it were an ordinary
galaxy, then it should be quite bright and would be visible with a
good amateur telescope.

"The ratio of dark matter to regular matter is at least 500-to-1,
which is higher than I would expect in an ordinary galaxy," Minchin
said. "However, it is very hard to know what to expect with such a
unique object - it may be that high ratios like this are necessary to
keep the gas from collapsing to form stars."

Long road to discovery

Other potential dark galaxies have been found previously, but closer
observations revealed stars in the mix. Intense visible-light
observations reveal no stars in VIRGOHI21.

The invisible galaxy is thought to lack stars because its density is
not high enough to trigger starbirth, the astronomers said.

The discovery was made in 2000 with the University of Manchester's
Lovell Telescope, and the astronomers have worked since then to verify
the work. It was announced Wednesday.

"The universe has all sorts of secrets still to reveal to us, but this
shows that we are beginning to understand how to look at it in the
right way," said astronomer Jon Davies of Cardiff University. "It's a
really exciting discovery."

Additional radio observations were made with the Arecibo Observatory
in Puerto Rico. Follow-up optical work was done with the Isaac Newton
Telescope in La Palma. Astronomers from Britain, France, Italy and
Australia contributed to the research. The project is now searching
for other possible dark galaxies.

Dark matter makes up about 23 percent of the universe's mass-energy
budget. Normal matter, the stuff of stars, planets and people,
contributes just 4 percent. The rest of the universe is driven by an
even more mysterious thing called dark energy.

Jim Hutton wrote:
Isn't this a matter of semantics?
Like if a husband says something in a forest with no wife within
earshot, is he still wrong? :-)


Yessir--Nature is the way she is completely independent of humans...
Well... not according to N. Bohr.

GM wrote:
So... when will we see proof of 'dark energy' mentioned in this
article:


The proof of any theory comes after the theory is proposed. Here is my
take on these new developments:

0% visible energy
4% visible matter
23% invisible matter
____________________
27% matter
=
73% invisible energy

Hypothesis:

It has become obvious that our universe consists primarily of dark
matter and dark energy, so it should be fairly obvious as well today
that visible matter is the product of dark matter and visible matter
interactions, and that "dark" energy is the vehicle by which these
interactions occur.

My model of the universe predicts that dark matter and energy comprise
space where interactions occur between lightwaves and dark matter
particles to create light, or, emr. Lightwaves collide with negative
matter particles (dark matter) and impart to them sufficient positive
energy as to transform them into real (visible) particles which we see
as "light".

Even more astounding that that, perhaps, is my hypothesis that
gravitation is not an attractive force at all, but a repulsive force
which prevents the amassing of real matter any larger than that which
corresponds to the particular situations of discrete matter or systems.

It is possible also that the there is an attractive force between
massive objects which is mediated by the repulsive forces of dark
matter to the extent that matter is forced to speed apart from other
matter such that it may appear that space is in a process of expansion.

As for the invisible dark energy, all energy is invisible to us. We do
not ever see energy; we see it only as motions of real objects when
energy is in use, and when it is in a stored form, we see only the
vessel in which it is stored. Energy is, like dark matter, only
detected by us by the effects it has on visible matter.

Thus, dark matter is negative mass (a la George Gamow) having negative
energy, which may interact with matter having positive mass and energy.


The basis of emr is temperature, and we can say that heat is thermal
radiation, which produces energy in the form of lightwaves. However,
emr is considered to be particle radiation, not wave radiation. My
model resolves that obstacle by having space comprised of dark matter
particle which interact with light wave energy to create light.

TomGee 02/24/05



Astronomers detect first invisible galaxy
Breakthrough could shed light on dark-matter mystery
By Robert Roy Britt
Senior science writer, Space.com

Astronomers have discovered an invisible galaxy that could be the
first of many that will help unravel one of the universe's greatest
mysteries.

The object appears to be made mostly of "dark matter," material of an
unknown nature that can't be seen.

Theorists have long said most of the universe is made of dark matter.
Its presence is required to explain the extra gravitational force
that
is observed to hold regular galaxies together and that also binds
large clusters of galaxies.

Theorists also believe knots of dark matter were integral to the
formation of the first stars and galaxies. In the early universe,
dark
matter condensed like water droplets on a spider web, the thinking
goes. Regular matter - mostly hydrogen gas - was gravitationally
attracted to a dark matter knot, and when the density became great
enough, a star would form, marking the birth of a galaxy.

The theory suggests that pockets of pure dark matter ought to remain
sprinkled across the cosmos. In 2001, a team led by Neil Trentham of
the University of Cambridge predicted the presence of entire dark
galaxies.

One of perhaps many

The newfound dark galaxy was detected with radio telescopes. Similar
objects could be very common or very rare, said Robert Minchin of
Cardiff University in Wales.

"If they are the missing dark matter halos predicted by galaxy
formation simulations but not found in optical surveys, then there
could be more dark galaxies than ordinary ones," Minchin told
Space.com.

In a cluster of galaxies known as Virgo, 50 million light-years away,
Minchin and colleagues looked for radio-wavelength radiation coming
from hydrogen gas. They found a well of it that contains a hundred
million times the mass of the sun. It is now named VIRGOHI21.

The well of material rotates too quickly to be explained by the
observed amount of gas. Something else must serve as gravitational
glue.

"From the speed it is spinning, we realized that VIRGOHI21 was a
thousand times more massive than could be accounted for by the
observed hydrogen atoms alone," Minchin said. "If it were an ordinary
galaxy, then it should be quite bright and would be visible with a
good amateur telescope.

"The ratio of dark matter to regular matter is at least 500-to-1,
which is higher than I would expect in an ordinary galaxy," Minchin
said. "However, it is very hard to know what to expect with such a
unique object - it may be that high ratios like this are necessary to
keep the gas from collapsing to form stars."

Long road to discovery

Other potential dark galaxies have been found previously, but closer
observations revealed stars in the mix. Intense visible-light
observations reveal no stars in VIRGOHI21.

The invisible galaxy is thought to lack stars because its density is
not high enough to trigger starbirth, the astronomers said.

The discovery was made in 2000 with the University of Manchester's
Lovell Telescope, and the astronomers have worked since then to
verify
the work. It was announced Wednesday.

"The universe has all sorts of secrets still to reveal to us, but
this
shows that we are beginning to understand how to look at it in the
right way," said astronomer Jon Davies of Cardiff University. "It's a
really exciting discovery."

Additional radio observations were made with the Arecibo Observatory
in Puerto Rico. Follow-up optical work was done with the Isaac Newton
Telescope in La Palma. Astronomers from Britain, France, Italy and
Australia contributed to the research. The project is now searching
for other possible dark galaxies.

Dark matter makes up about 23 percent of the universe's mass-energy
budget. Normal matter, the stuff of stars, planets and people,
contributes just 4 percent. The rest of the universe is driven by an
even more mysterious thing called dark energy.

"Mike Dworetsky" ) writes:
"Gautam Majumdar" wrote in message
. uk...
On Thu, 24 Feb 2005 05:39:19 +0000, MrPepper11 wrote:

nature.com
23 February 2005

Astronomers spot invisible galaxy
Discovery supports most recent theories about exotic dark matter Mark
Peplow

A galaxy that is made almost entirely of dark matter has been
discovered. It's the first galaxy found to have no stars at all, but it
fits well with predictions made by astrophysicists about where the
Universe's missing mass should be.

Why should it be called a "galaxy" and not just a rotating gas cloud or a
rotating cloud of dark matter ?

Dictionaries say a galaxy contains star, gas, dust, etc.


Good point, but maybe it has some faint stars not detectable yet. The INT
is a relatively small telescope, and if the "galaxy" contained only old,
faint stars such as those found in globular clusters, but spread thinly in
space, I'm not sure they could be detected that far away without very
special efforts being made--and maybe not even then. Such stars would be
individually as faint as 30th mag (a quick and rough guess).

A galaxy does not have to contain gas and dust to be so called--most
elliptical galaxies have very little of either, but we still call them
galaxies. But they ought to have at least some stars...


The tale may have grown in the telling. Note that the title of the
orginal paper talks about a dark cloud, not a galaxy.

-John Park