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by Andy Lloyd
from
DarkStar1 Website
Spanish version
Until fairly recently our knowledge of stars and planets was pretty
straightforward.
Stars shone, emitting light by hydrogen fusion
processes, and planets were dark objects orbiting them.
This was
simply common sense. No one spent too many sleepless nights worrying
about what would happen when a object, undergoing the process of gas
accretion to form a star or planet, would end up with mass somewhere
in between. There is a critical size of about 80 Jupiter masses
where such a body can sustain hydrogen fusion due to the
temperatures and pressures generated by its own gravity (1).
Then a
star is born. The formation of planets is less well understood, and
the emerging discoveries of extra-solar planets are challenging astro-physicists to revise their theories. Nevertheless, when a
planet is forming, up to several Jupiter masses in size, then it
remains simply that: a planet.
As the mass increases, things start
to get more complicated.
Sagan, Shapley & Marley
The concept of brown dwarfs has been banded about for some time,
although no reliable astronomical data has been available until
quite recently.
Carl Sagan enigmatically quotes a 1950s description
of a brown dwarf in his 1995 book "Pale Blue Dot":
"In the 1950s, it was suggested by the astronomer Harlow Shapley of
Harvard that brown dwarfs - he called them "Lilliputian stars" -
were inhabited. He pictured their surfaces as warm as a June day in
Cambridge, with lots of area. They would be stars that humans could
survive on and explore."(2)
What makes this quote strange is that Sagan’s knowledge of the
nature of brown dwarfs must have been vastly superior to this dated,
naïve view of Shapley’s.
So why use it when it was obviously so
misleading? He didn’t mitigate this with offering a more modern
viewpoint of the nature of failed stars.
I posed this question to Dr
Mark Marley, an academic specializing in the study of brown dwarfs,
and this was his reply:
"I looked up the quote in the book and agree with you that it really
isn't relevant. But when Sagan wrote
the book there was only indirect evidence of brown dwarfs. Today we
know they exist and know that indeed they are much like Jupiter.
When he wrote the book, it was possible, though not likely, that
brown dwarfs could be somewhat earth-like.
We know today this is not
the case. If I were writing the book, knowing what was known at that
time, I would not have included the quote.
Note that while brown dwarfs are not inhabitable, they might have
moons that might be inhabitable."(3)
Quite so. I should state here that Mark Marley is not endorsing my
work in any way, and was just giving me a few helpful answers to my
questions regarding brown dwarfs.
His answer does include this
invaluable statement that life could be possible on the moons of a
brown dwarf, however.
When Brown means Red
The term "brown dwarf" was first used by
Jill Tarter, of the SETI
institute, in her 1975 PhD thesis, in order to correct the use of
the previous term "black dwarf".
As she says:
"The use of the term ‘black dwarf’ was inappropriate because it had
already been used to describe the end phase of a fully evolved star
as it cooled from the white dwarf stage." (1)
Brown dwarfs are very difficult to find.
They "glow only faintly",
emitting most of their radiation in the infra-red bands. This is
because they are below the 0.08 solar-mass stellar limit, and fail
to ignite as stars in their own right. Instead, they emit radiation
from energy left over from their formation.
During the life-span of
a brown dwarf, the younger they are, the brighter they appear.
So we
have more chance of discovering brown dwarfs that have just formed.
As they get older, they start to appear more like Jupiter, only much
more massive. In general, a brown dwarf’s luminosity is expected to
be about a hundred thousandth of the Sun’s (4). Its spectral
characteristics are different to those of very cool stars, unusually
showing an absorption line of the short-lived element lithium.
Contrary to the description implied by its name, brown dwarfs appear
red, very red. A brown dwarf was discovered in the Solar vicinity by
Maria Theresa Ruiz of the European Southern Observatory in 1997, a
discovery that offers the potential for much better study of these
elusive objects.
She called it
KELU-1, the term for ‘red’ in the
language of the indigenous population of central Chile.
Although it is at a distance of 33 light-years, its visual magnitude
is 22.3, which is the sort of brightness projected for Murray’s
proposed brown dwarf in the Oort cloud.
This sets a precedent for
its discovery. (5)
Brown Dwarf Discoveries
The best known brown dwarf, and one that we can actually look at
through an Earth-bound 60-inch telescope, is
Gliese 229B, discovered
in 1995. This one is in a binary system with the low-mass red dwarf Gliese 229A, at a distance of just 19 light-years from the Sun.
The separation between the brown dwarf and its companion star is
about the same as that between the Sun and Pluto.
Its luminosity is
about one tenth of the faintest star.
Its spectrum has large amounts
of methane and water vapor. Methane could not exist if the surface
temperature were above 1500K.
Astronomers consider its temperature to be about 900K (compared to
Jupiter’s 130K), its mass to be between 20 and 55 Jupiters, and the
age of the binary system to be between 1 and 5 billion years old.
It
has a smoggy haze layer deep in its atmosphere, essentially making
it,
"much fainter in visible light than it would otherwise be".
It is possible that ultra-violet light from its companion star
changes its atmospheric properties from those of an isolated brown
dwarf, such as KELU-1.(1) The above image shows 3 brown dwarfs
compared with Jupiter, the Sun and the red dwarf Gliese A (6).
Note
the much higher temperatures of these brown dwarfs compared to
Jupiter.
So brown dwarfs emit visible light, albeit faintly, but are cool
enough to retain a planet like atmosphere! Stars and planets no
longer appear to be entirely different entities. Imagine living on a
moon of a brown dwarf : the dark star would be emitting red light
and heat, yet it would appear like Jupiter regarding size and
atmospheric consistency.
Rather like Jupiter on fire, perhaps!
Your
moon would not only be warmed by the intense infra-red emitted from
the brown dwarf, but also by its tidal effects (like
Io and
Europa
are warmed by the otherwise cool Jupiter), and by its ambient red
light.
If your moon was terrestrial, in other words had aqueous oceans and
a nitrogen-rich atmosphere, could not the emergence of life there be
entirely possible? Mark Marley seems to think so.
Without the
dangerous ultra-violet radiation and cosmic rays emitted by the Sun,
one could argue that this sort of environment is actually preferable
to the environment on Earth!
Coronal Flares
On 11th July (1995?), Reuters released news about the surprising discovery
of a ‘Solar Flare’ emitted by a near-by brown dwarf, known as
LP
944-20.
These new findings seem to back up the assertion that brown
dwarfs can act like stars as well as planets, albeit on a different
level of magnitude than our Sun. Note that the brown dwarf in
question is quite a sizeable one, however, and would be expected to
be more star-like than one that is only a few times the size of
Jupiter.
Nevertheless, this type of activity is clearly evident on a
failed star that is incapable of sustaining its own nuclear fusion:
 "A famous failed star known as a brown dwarf sent out a surprising
X-ray flare, astounding scientists who were expecting nothing more
than a few flickers, U.S. researchers said on Tuesday. The dwarf in
question, known as LP 944-20, is one of the best known and most
studied by astronomers because it is just 16 light-years from Earth.
This is quite close in cosmic terms, but because brown dwarfs are so
dim, it is visible from Earth - with a telescope - only as a tiny
dot of light. However, scientists can learn about these dim objects
by observing the X-rays they emit.
This brown dwarf has a mass about
60 times the mass of Jupiter but only 6 percent of the Sun's mass,
putting it under the threshold of mass that could make it a real
star.
Using NASA's orbiting
Chandra X-Ray Observatory, astronomers watched
LP 944-20 over a 12-hour period last December. For the first nine
hours, they saw no X-rays, then detected a dramatic flare before it
faded away over the next two hours.
The flare was comparable to a
small solar flare, but a billion times greater than X-ray flares
detected emanating from Jupiter, the National Aeronautics and Space
Administration said in a statement."
Lars Bildsten of the University of California, Santa Barbara, said
the flare is probably related to tangled magnetic fields beneath the
surface of the brown dwarf, which seem to be able to generate
X-rays.
Brown dwarfs "appear to live a more exciting life than we
presumed,'' Bildsten said in a telephone interview. "They are too
big to be planets and two small to be stars, but it does appear that
if you watch one it has very active events... there is action going
on.''
The X-ray flare the scientists saw was far beyond what
scientists had expected, Bildsten said in a statement:
"It was as
if we were searching for a dim bulb and instead found a bright flash
of light.'' (7)
This evidence is in keeping with my proposals about the Dark Star
Nibiru, and seems to swing the argument about brown dwarfs from the
‘planet’ identity towards the ‘star’ identity. The passages in the
Enuma Elish that describe Nibiru as having a ‘halo’, etc,
fit well
with this solar flare evidence.
Brown dwarfs, although dim, are
clearly emitting light to some degree.
The Searching Begins
Astronomers are actively seeking out brown dwarfs in the position of
the sky that the Dark Star theory predicts holds the hidden Nibiru.
In October 2001 European astronomers located a field of young brown
dwarfs in Ophiuchus, the constellation that Nibiru would move slowly
into after achieving its aphelion destination in Aquila (this
occurred during the 19th Century):
"Amid space clouds stuffed with baby stars, astronomers have
detected 30 difficult-to-spot brown dwarfs, failed stars that emit
very little radiation. The dusty clouds are near the star
rho
Ophiuchi, located 540 light-years away in the constellation of
Ophiucus.
Nesting in these clouds are more than 100 newborn stars -
large, bright and obvious. But using the European Space Agency's
Infrared Space Observatory (ISO), astronomers also detected the
faint heat signatures of the brown dwarfs." (8)
The astronomers say that they will return to this star-field for a
closer look at these brown dwarfs.
Given the unique stellar
signature of these celestial entities, one wonders whether they may
inadvertently stumble across a planet-sized brown dwarf that is to
be found much, much closer than these distant specimens.
 Brown Dwarf Imaged Orbiting Star
For the very first time an object orbiting another star has been
imaged, despite lying within the intense glare of the parent sun.
The brown dwarf is 'more than 12 times the mass of all the planets
in the solar system', and is orbiting the star
15-Sge at a distance
of 14 Astronomical Units, equivalent to an orbit that would lie
between Saturn and Uranus in our own system.
"This discovery implies that brown dwarf companions to average,
sun-like stars exist at a separation comparable to the distance
between the sun and the outer planets in our solar system," said
University of Hawaii astronomer Michael Liu.(9)
The searches for planets orbiting other stars had thus far failed to
reveal brown dwarfs, presumably as the range of orbital radius
sought was limited to 4AU. This new finding is the equivalent of an
'outer star system' planet, rather than the 'inner star system'
worlds previously discovered.
The sheer size of the brown dwarf
orbiting 15-Sge brings our knowledge of the formation of the outer
planets into further doubt:
 "This companion is probably too massive to have formed the way we
believe that planets do, namely from a circumstellar disk of gas and
dust when the star was young," Liu said in a statement.
"This
finding suggests that a diversity of processes act to populate the
outer regions of other systems."(9)
What is more exciting about this finding is the potential for this
brown dwarf to be imaged more precisely over time.
Does the coronal
discharge emitted by this dark star interact with the Stellar Wind
moving away from 15-Sge?
If the brown dwarf has an anomalous
appearance, then we should be able to compare this with my
theoretical model for the appearance of
Nibiru while at a similar
distance from the Sun.
Planets around Brown Dwarfs
A NASA artist impression
Scientific confirmation that planets might
form around interstellar brown dwarfs, in a similar way to those
that form around regular stars, emerged in 2001.
Accretion discs
were detected around these failed stars, some of which were as small
as 10 Jupiter masses. This led to speculation that some
free-floating brown dwarfs might harbor planets. Could some of them
be life-supporting?
Charles J. Lada, an astrophysicist at the Smithsonian Astrophysical
Observatory, thinks not.
A planet at the distance of Earth around a
brown dwarf would be frozen due to the smaller light and heat output
of the failed star compared to our Sun, he points out.
This was a question that was not addressed
during the now familiar distancing of 'serious' research from
the E.T. question.
Still, the scientific speculation by the Smithsonian
astrophysicists went much further than the normal cautious
skepticism:
"As for nearby brown dwarfs, the closest free-floating brown dwarfs
discovered so far (in a separate study) is about 13 light years from
Earth, and researchers expect to find much closer brown dwarfs in
the future, possibly within one light year of our Solar System. If
brown dwarfs do in fact exist so near our Solar System, it stands to
reason that they might also harbor planets.
For now, the closest
candidate object for harboring planets was Alpha Centauri, which is
4.3 light years away. The brown dwarf finding offers a mechanism for
generating a planet just outside our Solar System." (10)
Some scientists do seem to be waking up to the possibilities.
But we
can actually go much further than this. During the life of the solar
system, stars and interstellar brown dwarfs would have passed
through the solar system, as Jack Hills calculated in 1981 (11).
One
may well have been captured, by the mechanism Hills described in
1985 (12). Perhaps one that was long ago given the name 'Nibiru/Marduk'.
A bit further down this page, we will read of the direct observation
made in 2005 of a small Brown Dwarf's proto-planetary disc, offering
compelling evidence that these failed stars come with their own
planetary systems.
Orbiting Brown Dwarf Imaged
(22nd May 2002)
Brown dwarfs have not been found orbiting 'standard' stars within
5AU distance, but astronomers have strangely imaged one of these
celestial objects orbiting a
 low mass star called
LHS 2397a.
Current
theories have it that brown dwarfs are likely to be wandering
objects ejected from star systems early on in their development, but
this discovery indicates that this may need some revision.
Why one
has been found orbiting a loss mass star when they are conspicuous
by their absence around Sun-like stars is anyone's guess. But this
unexpected development has given astronomers a unique opportunity to
photograph the brown dwarf companion. For the low level of
luminosity of LHS 2397a allows the feeble light of the brown dwarf
to be separated, as this remarkable image shows.
What is more
exciting is that the separation of this brown dwarf from the low
mass star is only 3AU.
Comment that was passed on this discovery also provides some
interesting reading.
"We find companions to low-mass stars are typically only 4 AU from
their primary stars, this is surprisingly close together," said team
member Nick Siegler, a University of Arizona graduate student.
"More
massive binaries have typical separations closer to 30 AU, and many
binaries are much wider than this." The new Gemini observations,
Close said, "imply strongly that low-mass stars do not have
companions that are far from their primaries."
Similar results had been found previously by a team led by Dr.
Eduardo L. Martin of the University of Hawaii Institute for
Astronomy in a survey of 34 very low-mass stars and brown dwarfs in
the Pleiades cluster carried out with the Hubble Space Telescope.
These two surveys together clearly demonstrate that there is an
intriguing dearth of brown dwarfs at separations larger than 20 AU
from very low-mass stars and other brown dwarfs" (13)
Weather Patterns Might Explain
Anomalous Brightness of Brown Dwarfs
(25/5/02)
Brown dwarf experts have been trying to explain why many of these
objects are brighter than they should theoretically be.
Common sense
would dictate that as brown dwarfs cool over time, from their
initial
fiery beginnings, their relative brightness should also lessen
accordingly. Apparently not.
Using weather models derived from
Jupiter's own atmospheric system, and applying them to brown dwarfs,
a model has emerged that might explain the anomaly:
"Not massive enough to sustain the burning of hydrogen, like stars,
brown dwarfs go through cooling stages that scientists observe with
infrared energy-detecting telescopes. They appear as a faint glow,
like an ember from a fire that gives off both heat and light energy
as it dims.
Astronomers expected brown dwarfs, like most objects in the
universe, to grow steadily fainter as they cool. However, new
observations showed that during a relatively short phase, brown
dwarfs appear to get brighter as they cool. The explanation lies in
the clouds. At least 25,000 times fainter than the sun, brown dwarfs
are still incredibly hot, with temperatures as high as 3,140 degrees
Fahrenheit (2,000 degrees Kelvin).
At such high temperatures,
substances such as iron and sand are in gaseous form. As brown
dwarfs cool, these gases condense in the atmosphere into liquid
droplets to form clouds, similar to water clouds on Earth.
As the brown dwarf cools further, atmospheric weather patterns cause
a rapid clearing of the clouds; as the clouds are whisked away by
the storms, bright infrared light from the hotter atmosphere beneath
the clouds escapes, accounting for the unusual brightening of the
brown dwarfs.
'The model developed by the
group for the first time matches the characteristics of a
very broad range of brown dwarfs, but only if cloud clearing
is considered,' Burgasser said.
'While many groups
have hinted that cloud structures and weather phenomena should be
present, we believe we have actually shown that weather is present
and can be quite dramatic'." (14)
I've often likened the appearance of Nibiru to a planet that
smolders like embers.
Given the vivid description cited above, I
appear to be justified in making this remark. Even if Nibiru is very
old, and therefore a cool example of a brown dwarf, I think this
research is helpful.
After all, if Nibiru enters the solar system
during perihelion, the warming it will experience as a result could
readily set off immense storms in its atmosphere, and the above
model might allow us to predict how that could lead to an increase
in Nibiru's emission of light and heat.
The planet Nibiru at
perihelion would appear like a re-lit ember, apparently as a result
of its clearing cloud cover!
The Phoenix Effect
(15/4/03)
If the Sun does indeed have a massive solar companion that's on the
borderline between a massive planet and a small brown dwarf, then
how would it appear to observers as it comes into the solar system
at perihelion?
The answer to that question depends very much on the
age of the brown dwarf, but it is often stated that an old dwarf
would be essentially extinguished. So if Nibiru, which is roughly
the same age as the Sun (given that it entered the solar system only
half a billion years after its creation and so probably came from
the same stellar nursery), is a small brown dwarf it should be like
Jupiter. So the argument goes.
Of course, we don't know this for sure, because old small brown
dwarfs haven't yet been detected, being too dim capture by our
current telescopes. But there are indications that we are
under-estimating the potential energy output of the brown dwarfs
that are little more than massive Jupiters.
The recent capture of
X-ray activity from the small born dwarf
TWA 5B by the Chandra
telescope is a case in point:
"A Chandra observation revealed X-rays produced by TWA 5B, a brown
dwarf orbiting a young binary star system known as TWA 5A. The star
system is 180 light years from the Earth and a member of a group of
about a dozen young stars in the constellation Hydra.
The brown
dwarf orbits the binary star system at a distance about 2.75 times
that of Pluto's orbit around the Sun.
"Young brown dwarfs, like young stars, have turbulent interiors.
When combined with rapid rotation, this turbulent motion can lead to
a tangled magnetic field that can heat their upper atmospheres, or
coronas, to a few million degrees Celsius. The X-rays from both TWA
5A and TWA 5B are from their hot coronas.
TWA 5B is estimated to be only between 15 and 40 times the mass of
Jupiter, making it one of the least massive brown dwarfs known.
Its
mass is rather near the boundary (about 12 Jupiter masses) between
planets and brown dwarfs, so these results could have implications
for the possible X-ray detection of very massive planets around
stars" (15)
The fact that the emission is from the hot corona of the brown dwarf
is also very interesting, because the shape of the corona could be
subject to the stellar wind of the main star.
In Nibiru's case this
could lead to a cometary tail of fire in the shape of a planetary
magnetosphere swept back away from the Sun on its perihelion
approach. Hence the Phoenix effect.
Does the image from Chandra show
such an effect? Unfortunately the resolution and overall glare is a
major problem to answering such a question.
But this information is
encouraging nonetheless.
"This brown dwarf is as bright as the Sun today in X-ray light,
while it is fifty times less massive than the Sun," said Tsuboi.
"This observation, thus, raises the possibility that even massive
planets might emit X-rays by themselves during their youth!"
This research on TWA 5B also provides a link between an active X-ray
state in young brown dwarfs (about 1 million years old) and a later,
quieter period of brown dwarfs when they reach ages of 500 million
to a billion years." (16)
These certainly are interesting times...
From the Horse's Mouth
(14th May 2003)
For a little while I have been working closely with a researcher
called Rajasun.
Although he is not an academic astronomer, his
long-term interest in the idea of our solar system being a 'binary'
has propelled him headlong into the study of astrophysics. Recently,
he wrote to one of the foremost experts on brown dwarfs, J.D.
Kirkpatrick, and asked, amongst other things, whether an old, small
brown dwarf was still capable of 'flaring'.
It now seems that if,
for instance, Nibiru was a small brown dwarf of a similar age to our
Sun, then one might still expect flaring,
"because of the intense
surface gravity which consequently affects magnetic activity on the
brown dwarf" (Raja's words).
Raja: "Is the incidence/frequency of X-ray flares directly related
to Age and Teff of a BD [brown dwarf]? Is there a relationship
between the reduction of X-ray flaring activity and increased radio
flares on BDs (i.e. decreasing X-ray flaring leading to increase
incidence of Radio flares)?"
J.D.K. "That's precisely what we've been trying to determine, but
the brown dwarf community hasn't received much time to investigate
these issues using telescopes like Chandra and XMM. Keep in mind
that part of our inability to answer this question comes from the
fact that brown dwarfs, even when flaring, are pretty darned faint
in X-rays. Chandra and XMM have been reluctant to give time for
these projects because most brown dwarfs will be totally invisible
at X-ray wavelengths unless you get lucky and happen to catch one
during a flare."
Dr Kirkpatrick kindly recommended this helpful artist's rendition of
brown dwarf types:
"All objects are plotted to the same scale.
On the far left is the
limb of the Sun. To its right is shown a very low mass star (a
so-called "late-M dwarf"), a couple of brown dwarfs (a hotter "L
dwarf" and a cooler "T dwarf"), and the planet Jupiter. These
objects have masses ranging from 1050 times that of Jupiter (for the
Sun) through 75, 65, 30, and 1 Jupiter mass for the late-M dwarf, L
dwarf, T dwarf, and Jupiter, respectively.
The colors of the brown
dwarfs are chosen to match an age of 1 billion years. Despite the
range in mass, all four of the low-mass objects are approximately
the same size, ten times smaller than the diameter of the Sun.
[This
image] shows how these objects might appear to the human eye: the M
and L dwarfs are red, while the T dwarf is dimly magenta, due to
lack of light - actually absorptions by sodium and potassium atoms
- in the green portion of the spectrum." (17)
He also recommended a recent paper by Adam Burrows, et al, regarding
theoretical modeling of brown dwarfs.
It had these remarkable lines
in its extract:
"These changes suggest physical reasons to expect
the emergence of at least one new stellar class beyond the
T dwarfs.
Our spectral models populate, with cooler brown dwarfs having
progressively more planet-like features, the theoretical gap between
the known T dwarfs and the known giant planets. Such objects likely
inhabit the galaxy, but their numbers are as yet unknown." (18)
All of which seems to suggest that old brown dwarfs cannot simply be
consigned to the dustbin of planethood.
There is a growing
flexibility built into these considerations that allows for
planet-like old brown dwarfs with remnant stellar characteristics.
This would readily fit the picture of a binary companion to our Sun
that had so far evaded detection, but was yet capable of quite a few
surprises.
Nibiru-like Binary Discovered
(11th July 2004)
The chance discovery of a binary brown dwarf system has increased
the potential for a similarly widely separate binary system for our
Sun.
The two brown dwarfs are separated by about 240 AU, or 240
times the distance between the Sun and the Earth. This would relate
to a semi-major axis distance for an orbit of 3500 years, similar to
that envisioned for Nibiru. This is a very rare find, and breaks the
mould for such binary systems, which tend to be separated distances
that are a fraction of this.
Astronomers are generally skeptical
about finding planets at this distance, because they believe that
the orbits would be easily subject to perturbation, and the binaries
would break down.
This discovery must bring this long-held belief into question.
The
discovery was made by Kevin Luhman, from Harvard University,
Massachusetts. Seeking young brown dwarf for study he trained the
Magellan telescopes at Chile's Las Campanas Observatory on a star
cluster 540 light years away in the Chameleon constellation.
He
found a binary pair of brown dwarfs, and this discovery has
subsequently re-opened the debate about how brown dwarfs form.
"Calculations showed that the two brown dwarfs were orbiting each
other at 240 times the distance between the Earth and Sun, a
distance 10 times greater than other brown dwarfs pairs.
"Since even the slightest tug could upset this fragile balance,
Luhman suggests the pair could not have formed from a violent
ejection. Instead, they must have formed in a slow gravitational
collapse, like stars.
"Gibor Basri, an astronomer at the
University of California, Berkeley, and one of the early
pioneers of brown dwarf research, agrees. "The distance between
most other binaries is very small. The extremely large
separation in this binary shows that the same process that
formed stars extends to bodies of low mass as well." (19)
Other recent scientific findings suggest that
the Sun did indeed
once have a large body in orbit around it, larger than a Jovian
planet.
This discovery shows that a binary with a brown dwarf can
form at this distance, and remain stable. Which would suggest that
the presence of an ancient brown dwarf companion to the Sun need not
have been lost over time.
It may still be out there, and it may
describe an orbit that is tantalizingly close to that of the
mythical
Nibiru.
Small Brown Dwarfs have their Own Planets
(9th February 2005)
'New Scientist' has reported on a remarkable discovery about the
formation of a planetary system around a small Brown Dwarf.
Because
the glare of the Brown Dwarf is so much smaller than that of
'regular' stars it was possible to directly image material in a disc
around it. Some of this material was clumping indicating planet
formation. It is thought that the total mass of the proto-planetary
system orbiting a Brown Dwarf would be equivalent to about 10% of
the Dwarf's own mass.
That provides enough material to form a
Saturn-like planet, as well as a number of terrestrial worlds.
Artist's concept of brown dwarf disc
The Brown Dwarf in question
lies about 500 light years away in the sky region known to
astronomers as
Chamaeleon I, which is a known stellar nursery. The
disc was observed by the Spitzer telescope, appearing relatively
bright in the infra-red part of the spectrum.
The finding has fuelled speculation in the scientific community that
life-supporting planets might be discovered around Brown Dwarfs:
"The surface temperature of the mini brown dwarf is about 2000°C,
which means that any planet 1.5 to 7 million kilometers away could
maintain liquid water. The disc probably straddles this range"
(20)
Not only that, but discovering such worlds in these kinds of systems
might actually be easier than looking for planets in more classical
star systems, where the glare of the stare makes it very difficult
to image much of anything in its immediate vicinity. Just recently a
massive planet was imaged orbiting a brown dwarf (21).
The scientific team, led by Kevin Luhman of the Harvard-Smithsonian
Center for Astrophysics in Cambridge, Massachusetts, US, hopes to
extend its search to even smaller brown dwarfs to see how small they
can get yet still allow planetary formation.
Not only does this
research raise questions about how star and their planetary systems
develop, but it also opens the door to more urgent speculation about
the nature of a binary Brown Dwarf Companion in our own Solar
System, should such an object be discovered in the future.
The
potential for life to have developed in such a system is increasing;
at least, that is the verdict of science!
Brown Dwarf 'Sun' Finding
(5th March 2004)
As has already been mentioned on this page, brown dwarfs are massive
planets that have accreted many times the amount of mass than
Jupiter. Yet they remain approximately the same size. Instead, the
weight is confined to an area roughly the size of Jupiter, and this
makes them increasingly dense.
This, in turn, makes their activity
levels so much greater than mere gas giants like Jupiter as their
surface gravity builds and builds with greater and greater mass.
OGLE-TR-122b
Although this general idea was accepted, it was still thought that
the brown dwarfs would naturally increase in size as they moved
towards a more typical dwarf star, like a red dwarf.
However,
scientists on the
OGLE program have analyzed one particular binary
brown dwarf, which is closely orbiting a Sun-like star towards the
centre of the Milky Way, that is off the charts. They have
discovered, to their surprise, that this binary companion shines
like the Sun, yet is only 16% larger than Jupiter (22).
This is amazing, because the binary companion is 50 times as massive
as Jupiter, making it very dense indeed (23). Previously, brown
dwarfs of this magnitude were imagined to be much larger objects.
What is most surprising about this discovery is that this
'sub-stellar object' is simultaneously in the mass range of the
brown dwarfs, shines like the Sun but is the size of a regular
planet! How mixed up is that? Which, of course, goes to show that
there are many, many possibilities to these brown dwarf objects.
This here is a Dark Star that isn't even remotely dark...
Young Brown Dwarfs emit Massive Jets
(24th June 2005)
As time goes on, the consensus within the scientific community
appears to be that brown dwarfs form more like stars than planets.
They have been observed to have dusty disks of their own, and now
have been seen to emit hot jets of material, in a similar way to
more regular stars during the celestial birthing stage:
"Researchers, led by Emma Whelan of Ireland's
Dublin Institute for
Advanced Studies (DIAS), have observed a jet stretching 1.5 billion
kilometers from a young brown dwarf in a stellar nursery called Rho Ophiuchi. Similar jets have been detected around young, massive
stars and are thought to form from material in the disc that swirls
around them.
The stars grow when matter falls on them from the disc,
but the stars' magnetic fields funnel about a tenth of that matter
back through the jets.
This observation of a jet, combined with an
indirect detection of an apparently large disc around the brown
dwarf, suggests,
"they form like ordinary stars rather than being
ejected", says team member Thomas Ray of DIAS. "But it might end up
that brown dwarfs form by two methods." (24)
This has implications for
the Dark Star Theory.
Firstly, it
increases the likelihood that a brown dwarf embedded in the Solar
System would have developed as a star-like entity in its own right.
It may have done this as a loosely bound binary companion to the
Sun, within a fairly densely packed stellar nursery.
This makes good
sense anyway, because the chance of the Sun capturing an
interstellar companion in the form of an ejected planet-like brown
dwarf is quite remote. At least on a statistical level. This loosely
bound binary companion's orbit may have altered over time, bringing
it into close proximity to the Sun's planetary zone at some point
(probably during the 'late, great bombardment' about 3.9 billion
years ago).
Hence, it played a part in shaping the Sun' planetary
system, creating the various anomalies we find today.
The jets of material ejected by young brown dwarfs also serve to
indicate the remarkable activity levels of these objects, and the
real potential for star-like qualities for even oldish brown
dwarfs, like the own potentially orbiting our star.
I suspect they
have generally been underestimated.
Young Brown Dwarfs have Proto-planetary Discs
(21st October 2005)
Are brown dwarfs, planets or stars, or a bit of both?
They
increasingly resemble stellar class objects, and this has been
highlighted by the discovery of proto-planetary discs around several
classic brown dwarfs in the
Chamaeleon constellation.
"The astronomers discovered that five of the six disks contain dust
particles that have crystallized and are sticking together in what
may be the early phases of planet assembling. They found relatively
large grains and many small crystals of a mineral called olivine.
'We are seeing processed particles that are linking up and growing
in size,' said Dr. Ilaria Pascucci, a co-author also of the
University of Arizona. 'This is exciting because we weren't sure if
the disks of such cool objects would behave the same way that
stellar disks do.'
The team also noticed a flattening of the brown
dwarfs' disks, which is another sign that dust is gathering up into
planets." (25)
The potential for the study of planets forming in brown dwarf star
systems is huge.
-
Firstly, it is thought that brown dwarfs are as
numerous as traditional stars.
-
Secondly, in the case of a brown
dwarf system, the reflected light from candidate planets orbiting
brown dwarfs would not be so overwhelmed by the brilliant light of
the parent star. This would make it easier to differentiate smaller
planets in this kind of dwarf system, and to analyze the composition
of planetary atmospheres.
-
Thirdly, undiscovered brown dwarfs may
well lurk between here and the nearest stars, offering the potential
for the discovery of closer planets than previously thought.
Might a brown dwarf companion to the Sun remain undiscovered, with
its own system of planets? This new evidence at least suggests that
if a companion is out there, then it is probably not alone...
References
1) R. Naeye ‘Astronomy’ Aug 1999, p36-42
2) C. Sagan "Pale Blue Dot" p392 Headline Book Publishing
3) Correspondence from M. Marley, 28/1/00
4) David Griffin "How can we detect Brown Dwarfs?" 1998
5) ESO press release 7/97 "A Faint and Lonely Brown Dwarf in the
Solar Vicinity". http://www.eso.org/outreach/press-rel/pr-1997/pr-07-97.html
6) Thanks to James Monds
http://sci.esa.int/content/news/index.cfm?aid=18&cid=12&oid=28886
7) Reuters, 11 July 2000, By Deborah Zabarenko, Washington
8) "Nest of Elusive Brown Dwarfs Seen in Stellar Nursery" Thanks to
JJK and Damon Elkins http://space.com/scienceastronomy/astronomy/brown_dwarfs_011025.html
9) R. Stenger "In a first, object near a star caught on camera" 7
Jan 2002, with thanks to Allene Keller and Theo http://www.cnn.com/2002/TECH/space/01/07/brown.dwarf/index.html
10) R. Britt "Dark Planets May Orbit Strange Nearby Objects" 7th
June 2001, painting by B. Scott Kahler http://www.space.com/scienceastronomy/astronomy/aas_browndwarfs_010607.html
11) J. Hills Astron. J. 86, 1730 (1981)
12) J. Hills Astron. J. 90, 1876-1882 (1985)
13) "Brown Dwarf Found Orbiting Star at Earth-like Distance"
http://www.cosmiverse.com/news/space/space05210207.html
With thanks to Brant McLaughlin and David Pearson
14) Astronomers Find Jupiter-Like Weather On Brown Dwarfs
http://www.spacedaily.com/news/extrasolar-02l.html
Or http://www.ucla.edu/Templates/NewsItem1.html23rd May 2002 Thanks
to Brant
15) "TWA 5B: X-Rays Found From a Lightweight Brown Dwarf"
http://chandra.harvard.edu/photo/2003/twa5b/
With thanks to James Monds
16) "X-rays found from a lightweight brown dwarf"
http://www.spaceflightnow.com/news/n0304/14browndwarf/
17) "An Artist's View of Brown Dwarf Types" Dr. Robert Hurt of the
Infrared Processing and Analysis Center
http://spider.ipac.caltech.edu/staff/davy/2mass/science/comparison.html
18) A. Burrows et al "Beyond the T Dwarfs: Theoretical Spectra,
Colors, and Detectability of the Coolest Brown Dwarfs"
astro-ph/0304226 April 2003, with thanks to J.D. Kirkpatrick and
Rajasun
19) Amitabh Avasthi "Brown Dwarfs win Star Status" 9th July 2004
http://www.newscientist.com/news/news.jsp?id=ns99996133 With thanks
to David Pearson
20) Hazel Muir, "Brown dwarf may someday harbour habitable planets"
8th February 2005, http://www.newscientist.com/article.ns?id=dn6977
with thanks to Peter Gersten, among several others!
21) 'Astronomers discover beginnings of 'mini' Solar System'
JPL/NASA 7th February 2005
http://www.jpl.nasa.gov/news/news.cfm?release=2005-022 With thanks
to Monika Myers and James Monds
22) The Guardian "Hot Star Shines in Tiny Role" p11, 5th March 2005
23) Robert Roy Britt "Newfound star smaller than some planets" 3rd
March 2005 http://msnbc.msn.com/id/7081156/
24) Maggie McKee Violent jet detected spewing from brown dwarf"
24/6/05
http://www.newscientist.com/article.ns?id=dn7569&feedId=online-news_rss20
Nature (vol 435, p 652), with thanks to Shad Bolling and David
Pearson
25) Spitzer Press release "NASA's Spitzer Finds Failed Stars May
Succeed in Planet Business" 20th October 2005
http://www.spitzer.caltech.edu/Media/releases/ssc2005-21/release.shtml
-
"Dumping more mass on a brown dwarf doesn’t make it bigger, it
just makes it denser. A 70-Jupiter-mass and 20-Jupiter-mass brown
dwarf are both about the size of Jupiter.
-
From up close, a young brown dwarf would look like a low-mass
star, but an old brown dwarf would look more like Jupiter.
-
Brown dwarfs aren’t brown, they would look red to the naked eye.
-
Brown dwarfs radiate most of their energy in infra-red light.
-
There’s a 50:50 chance that a brown dwarf lurks within 4
light-years, the distance to the sun’s nearest stellar neighbour.
-
Some brown dwarfs spin so fast that they complete one rotation in
less than an hour.
-
Planets have rock-ice cores; brown dwarfs have hydrogen cores.
-
The average density of a brown dwarf is about 70 grams per cubic
centimeter, which is 5 times the density at the centre of the
Earth." (1)
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