***********************************
The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 277 2009 December 6
====================================================
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by
visiting http://www.popastro.com/
LEONIDS 2009
By Alastair McBeath, SPA Meteor Section Director
Leonid activity stronger than at most returns was reported for over
twenty-four hours from about 03:30 UT on November 17 to 05:00 UT
on the 18th this year, according to the latest preliminary International
Meteor Organization (IMO) findings, available at:
http://www.imo.net/live/leonids2009/ . Zenithal Hourly Rates (ZHRs)
were above 20 throughout that time, whereas the typical "normal"
activity is nearer 15 +/- 5. As reported last time, the general pattern,
showing two main peaks, has remained apparent within this day-long
enhancement, but the ZHR values have fallen significantly since that
initial article. The first peak still seems likely to have been centred near
20:15 UT on November 17, with ZHRs from about 19:55-20:30 holding
somewhat variably at ~75-90. Activity dropped to about 60 near 20:45,
before peaking again close to 21:00 UT with ZHRs of ~80. The very
best from this second maximum now seems to have been shorter than
the estimated circa 15-minutes after 21h suggested previously, with
ZHRs having fallen to ~70 before 21:15, though this level persisted
through till shortly after 21:30, dropping to ~60 and below thereafter.
This seeming "quarter-hour" precision is somewhat misleading,
because the IMO datapoints were given at roughly 15-minute intervals
during this time and for much of the period closest to the expected
maxima. Activity continued with ZHRs of ~40-55 until after 01h UT on
November 18, and dropped only slowly over the succeeding four hours.
There are suggestions for a couple of possible weaker submaxima
within this post-maxima period, but these would need a more detailed
analysis to confirm, as the variation is close to the probable errors
involved.
Other than in a very general way, with protractedly better-than-usual
activity during part of November 17-18 (which only a very few of the
theoreticians had predicted in advance), this observed behaviour fitted
quite poorly to the anticipated strongest Leonid activity, which most
agreed should have happened between 21h-22h UT on November 17,
probably within the 21:45-22:00 interval, and that ZHRs would be likely
~80-150 or more, with most favouring ~120-150+. Why these
discrepancies occurred is unknown, but they may relate to the age of
the Leonid dust trails involved. The two main trails were those
expected to have been laid-down at parent comet 55P/Tempel-Tuttle's
1466 and 1533 perihelion passages. A very slight change in the
comet's orbit since then, or somewhat different amounts of dust
emitted, and when, during the comet's perihelia, could all have affected
the theoretical expectations, but it is a curiosity that all the analysts
should have missed the actual peaks by about an hour, compared to
the consensus of predictions attained by different methods. If nothing
else, this reinforces the adage not to rely solely on predictions for when
meteor shower maxima may happen!
As noted last time, UK observers struggled with the weather across the
main part of the Leonids, but more reports have come through from
November 16-17 especially, confirming that parts of Northern Ireland
and central-southern England (Leics, Worcs, Oxon & Herts) were the
most favoured spots, and lucky observers towards the end of the night
then were recording ZHRs of about 25 +/- 3. Thanks to considerable
support from overseas meteor watchers, most notably those of the
North American Meteor Network, NAMN ( http://www.namnmeteors.org ),
results provided almost immediately after the event by NAMN leader
Mark Davis, hints of the improving rates during the morning UT hours of
November 17, with ZHRs of 30+ after 10h, were found in the Section's
analysis, along with part of the declining rates on the UT morning of
November 18. Sadly however, the very strongest activity was not visible
for our observers in either Europe or North America at this return.
Though the sky-quality many had to endure was not of the highest order,
magnitude distributions for 161 Leonids and 140 sporadics seen under
better conditions (limiting magnitude at least +5.4, cloud cover less
than 20%) suggested the Leonids may have been somewhat brighter
than normal near the peak, with mean magnitude values corrected to an
ideal sky of +2.2 and +3.4 respectively. The sporadic value was much
as expected. Too few train reports were received to analyse those, but
some excellent Leonid trains lasting from tens of seconds up to ten
minutes (and imaged in the latter instance, as mentioned last time)
were noted.
The contributing observers were as follows, including those who
reported casual data via the SPA and UK Weather World Forums (see
http://snipurl.com/tkkl2 and http://snipurl.com/tkkla respectively for more
details on those), where "I" means still-imaging, "R" radio and "V"
visual results were made by that individual:
Salvador Aguirre (Mexico; NAMN; V), "akkan" (England; V), Michael
Boschat (Nova Scotia, Canada; NAMN; V), Mark Davis (South
Carolina, USA; NAMN; V), David Entwistle (England; R + V), Bill
Godley (Oklahoma, USA; NAMN; V), Bill Haddon (California, USA;
NAMN; V), Alan Heath (England; R), Carl Hergenrother (Arizona, USA;
NAMN; V), Ken Hodonsky (Oklahoma, USA; NAMN; V), Mike Linnolt
(Hawaii, USA; NAMN; V), Andy Mayhew (England; I + V), "markh"
(England; I), Alastair McBeath (England; V), Martin McKenna (Northern
Ireland; I + V), Jane Mills (England; V), "OkarcheDave" (Oklahoma,
USA: V), Matthew Phipps (England; V), Richard Taibi (Maryland, USA;
V), William Watson (New York, USA; NAMN; V).
Very many thanks go to all involved so far. Anyone with Leonid data still
to submit, please do so as soon as possible!
NOVEMBER 21-22 IMAGED FIREBALLS
By Alastair McBeath, SPA Meteor Section Director
Two notable fireballs have been reported to the SPA from November
21-22, both of which were imaged. The first was at around 21:00 UT,
seen from numerous places in the Gauteng region of South Africa,
including Johannesburg and Pretoria. It was a brilliant, detonating event,
and was caught on CCTV by-chance. There are links to the video and
media reports via the UK Weather World's Space Weather Forum topic
here: http://snipurl.com/tkm5f .
The second was much closer to home, imaged by automated cameras
run by Armagh Observatory in Northern Ireland. This event was
estimated as brighter than magnitude -5, and happened at 00:57 UT.
Two UK radio meteor observers, Andy Smith in Devon and Richard
White in Northern Ireland, recorded near-simultaneous strong,
protracted echoes beginning at this time, which were likely produced
by the meteor. The Armagh website has more information on their
imaging of the fireball, at: http://snipurl.com/tkmin , while the video is
available here:http://snipurl.com/tkmit . Especial thanks go to Assistant
Meteor Director David Entwistle for rounding-up the information on this
meteor.
Any fresh observations of the "Armagh" fireball, or any others (a fireball
is any meteor of magnitude -3 or brighter), made from the British Isles
or nearby, would be welcomed by the Section. The minimum details I
need from you are:
1) Exactly where you were (give the name of the nearest town or large
village and county if in Britain, or your geographic latitude and longitude
if elsewhere in the world);
2) The date and timing of the event; and
3) Where the fireball started and ended in the sky, as accurately as
possible, or where the first and last points you could see of the trail
were if you did not see the whole flight.
More advice and a fuller set of details to send (including an e-mail
report form) are given on the "Making and Reporting Fireball
Observations" page of the SPA website, at: http://snipurl.com/tkklk .
Good luck to all for the Geminids!
MERCURY MISSION CLEARS HURDLE
BBC News
The European Space Agency (ESA) has approved greatly increased expense
for a mission to Mercury. BepiColombo, due for launch in 2014, was
supposed to cost ESA £595m, but the challenge of building a probe able
to survive the torrid heat and radiation it would suffer has pushed
the price up to £950m. It will be baked directly by the Sun,
receiving some 14,000 watts per square metre, about 10 times what a
spacecraft in orbit around the Earth receives. Developing systems that
that can cope with such an environment has led to the mission getting
heavier. Overall, the launch mass has grown from some three tons to
just over four tons, necessitating a larger, more expensive rocket --
an Ariane-5 instead of a Soyuz.
BepiColombo is a joint endeavour with the Japanese. Two probes will
travel to Mercury, and separate when they achieve orbit (in 2020).
Europe will produce a Mercury Planetary Orbiter which will be equipped
with 11 scientific instruments. Flying in a polar orbit, it will
study Mercury for at least a year, imaging the planet's surface,
generating height profiles, and collecting data on Mercury's
composition and wispy atmosphere. Japan will be responsible for the
Mercury Magnetospheric Orbiter. It will investigate the planet's
magnetic field with its five on- board instruments.
JUPITER SATELLITE NAMED
IAU
The IAU has announced that the 50th confirmed satellite of Jupiter,
S/2003 J 17, is to be named Herse.
V445 PUPPIS MAY BE A TYPE-1a SUPERNOVA PROGENITOR
ESO
The double-star system V445 Puppis is a candidate to become one of the
exploding stars known as Type Ia supernovae. V445 Puppis is the
first, and so far only, nova showing no evidence at all for hydrogen.
It provides the first evidence for an outburst on the surface of a
white dwarf dominated by helium. That is suggestive, as we know that
Type Ia supernovae lack hydrogen and the companion star in V445 Pup
also lacks hydrogen, instead dumping mainly helium onto the white
dwarf. In November 2000, the system underwent a nova outburst,
becoming 250 times brighter than before and ejecting a large quantity
of matter into space.
A supernova is one way that a star can end its life. One sort is
called Type Ia. A defining characteristic of Type Ia supernovae is
lack of hydrogen -- yet hydrogen is the most abundant element in the
Universe. Such supernovae most probably arise in systems composed of
two stars, one of which is a white dwarf. The white dwarf in such a
system can accumulate on its surface matter lost by its companion, but
usually only to a small extent before a surface explosion, that we see
as a nova outburst, occurs and ejects much, perhaps all, of the
accumulated matter back into space.
Astronomers have used an adaptive-optics instrument on the VLT to
obtain images of V445 Puppis over a time span of two years. The
images show a bipolar shell, initially with a very narrow waist, with
lobes on each side. The shell -- unlike any previously observed for a
nova -- is expanding at about 7000 km/s. A thick disc of dust, which
must have been produced during the outburst, obscures the two central
stars. Combining the images with data obtained with other telescopes,
the astronomers determined the distance of the system, about 25,000
light-years, and its intrinsic brightness, over 10,000 times brighter
than the Sun. That implies that the white dwarf has a high mass that
is near its fatal limit and is still being fed by its companion at a
high rate. Whether V445 Puppis will eventually explode as a
supernova, or whether the recent nova outburst has pre-empted that
pathway by ejecting too much matter back into space, is unknown.
SPITZER TELESCOPE OBSERVES YOUNG BROWN DWARFS
JPL
The Spitzer infrared space telescope has contributed to the discovery
of the youngest brown dwarfs ever observed. Brown dwarfs are less
massive and cooler than stars, but more massive (and normally warmer)
than planets. They are often called 'failed' stars, because they lack
the mass necessary to compress their cores to the point where they are
hot enough to ignite the nuclear fusion that burns hydrogen into
helium and powers most stars. They end up as cooler, less-luminous
objects that are difficult to detect. Moreover, young brown dwarfs
evolve rapidly, making it difficult to catch them when they are first
born. In fact, none has been seen in the earliest stages of formation
until now. Now, Spitzer's infrared camera has penetrated a dusty dark
cloud called Barnard 213, a region of the Taurus--Auriga interstellar-
cloud complex well known to astronomers as a hunting ground for young
objects, to observe not one but two of what seem likely to be the
faintest and coolest brown dwarfs ever observed. Observations with
other telescopes have helped to show that the two objects are still
inside the dusty envelope within which they formed.
DARK GALAXY COLLIDING WITH THE MILKY WAY
New Scientist
The Milky Way's neighbourhood may encompass many invisible galaxies,
one of which appears to be colliding with our own. In 2008, a cloud of
hydrogen with a mass then estimated at about 1 million Suns was found
to be colliding with our galaxy. Now it appears that the object is
massive enough to be a galaxy itself. Called Smith's Cloud, it has
managed to avoid disintegrating during its collision with our own,
much bigger galaxy. Furthermore, its trajectory suggests that it
passed through the disc of our galaxy once before, about 70 million
years ago. To have survived, it must contain much more matter than
previously thought, in order to provide enough gravity to hold itself
together. Calculations indicate that it has about 100 times the
previously estimated mass. Simulations of galaxy formation suggest
that a galaxy the size of the Milky Way should be accompanied by about
1000 dwarf galaxies, but only a few dozen have been found so far.
Some of the dwarfs which are (according to the simulation) missing may
be dark galaxies that are all-but invisible.
VESTIGE OF MILKY WAY'S BUILDING BLOCKS?
ESO
The galactic bulge is a troublesome region of our galaxy for
astronomical observations: only infrared light can penetrate its dust
clouds and reveal its myriads of stars. Observations made with the
VLT have shown an unusual mix of stars in a stellar grouping within
the bulge, known as Terzan 5. It appears that that object, unlike all
but a few exceptional globular clusters, does not consist of stars
that were all born at the same time, but formed in at least two
different episodes, about 12 billion and 6 billion years ago. Only
one globular cluster with a similar complex history of star formation
has been observed in the halo of the Milky Way, and that is Omega
Centauri. The new observations show that Terzan 5 is more massive
than previously thought: along with the complex composition and
troubled star-formation history of the system, that suggests that it
might be the surviving remnant of a disrupted proto-galaxy, which
merged with the Milky Way during its very early stages and thus
contributed to the formation of the galactic bulge.
UNIVERSE MAY BE PEPPERED WITH BLUE DWARF GALAXIES
Topix
Astronomers have discovered that the Universe is peppered with tiny
blue dwarf galaxies known as 'blue fuzzies'. The 'tiny' galaxies are
made up mostly of young hot stars that shine brightly, dominating the
light from the galaxies concerned. The discovery was made by
astronomers at the Anglo-Australian Observatory while examining data
from the 'Galaxy and Mass Assembly' survey (GAMA). The aim of the
survey is to map the structure in our local Universe much better than
previous surveys. It incorporates data from the Sloan Digital Sky
Survey, which contains more than 930,000 galaxies and 120,000 quasars,
and extends to approximately 2.5 billion light-years away. When the
astronomers obtained more detailed observations of one of the blue
fuzzies imaged by the survey, they was surprised to discover that it
was in fact an entire galaxy. Since that first discovery, the team
has examined about a hundred more blue fuzzies. The discovery
suggests that the 'nearby' Universe is not dominated by big galaxies
such as the Milky Way or Andromeda, but by lots of small ones.
The blue fuzzies are about the same size as the Small Magellanic
Cloud, averaging around 7000 light-years across and containing as much
mass as seven billion Suns. They are old galaxies, but unlike Milky-
Way-sized galaxies that form stars very rapidly, the blue fuzzies have
their stars forming at a slow but steady pace, giving them a frosting
of young hot stars. They are scattered fairly evenly throughout the
Universe at distances ranging out to seven hundred million light
years. While their distribution follows the voids and filaments which
make up the structure of the cosmos, they seem to be more common in
less-dense areas, away from the large galaxies and galaxy clusters.
Bulletin compiled by Clive Down
(c) 2009 the Society for Popular Astronomy
====================================================================The SOCIETY for POPULAR ASTRONOMY
***********************************
====================================================
Electronic News Bulletin No. 277 2009 December 6
====================================================
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by
visiting http://www.popastro.com/
LEONIDS 2009
By Alastair McBeath, SPA Meteor Section Director
Leonid activity stronger than at most returns was reported for over
twenty-four hours from about 03:30 UT on November 17 to 05:00 UT
on the 18th this year, according to the latest preliminary International
Meteor Organization (IMO) findings, available at:
http://www.imo.net/live/leonids2009/ . Zenithal Hourly Rates (ZHRs)
were above 20 throughout that time, whereas the typical "normal"
activity is nearer 15 +/- 5. As reported last time, the general pattern,
showing two main peaks, has remained apparent within this day-long
enhancement, but the ZHR values have fallen significantly since that
initial article. The first peak still seems likely to have been centred near
20:15 UT on November 17, with ZHRs from about 19:55-20:30 holding
somewhat variably at ~75-90. Activity dropped to about 60 near 20:45,
before peaking again close to 21:00 UT with ZHRs of ~80. The very
best from this second maximum now seems to have been shorter than
the estimated circa 15-minutes after 21h suggested previously, with
ZHRs having fallen to ~70 before 21:15, though this level persisted
through till shortly after 21:30, dropping to ~60 and below thereafter.
This seeming "quarter-hour" precision is somewhat misleading,
because the IMO datapoints were given at roughly 15-minute intervals
during this time and for much of the period closest to the expected
maxima. Activity continued with ZHRs of ~40-55 until after 01h UT on
November 18, and dropped only slowly over the succeeding four hours.
There are suggestions for a couple of possible weaker submaxima
within this post-maxima period, but these would need a more detailed
analysis to confirm, as the variation is close to the probable errors
involved.
Other than in a very general way, with protractedly better-than-usual
activity during part of November 17-18 (which only a very few of the
theoreticians had predicted in advance), this observed behaviour fitted
quite poorly to the anticipated strongest Leonid activity, which most
agreed should have happened between 21h-22h UT on November 17,
probably within the 21:45-22:00 interval, and that ZHRs would be likely
~80-150 or more, with most favouring ~120-150+. Why these
discrepancies occurred is unknown, but they may relate to the age of
the Leonid dust trails involved. The two main trails were those
expected to have been laid-down at parent comet 55P/Tempel-Tuttle's
1466 and 1533 perihelion passages. A very slight change in the
comet's orbit since then, or somewhat different amounts of dust
emitted, and when, during the comet's perihelia, could all have affected
the theoretical expectations, but it is a curiosity that all the analysts
should have missed the actual peaks by about an hour, compared to
the consensus of predictions attained by different methods. If nothing
else, this reinforces the adage not to rely solely on predictions for when
meteor shower maxima may happen!
As noted last time, UK observers struggled with the weather across the
main part of the Leonids, but more reports have come through from
November 16-17 especially, confirming that parts of Northern Ireland
and central-southern England (Leics, Worcs, Oxon & Herts) were the
most favoured spots, and lucky observers towards the end of the night
then were recording ZHRs of about 25 +/- 3. Thanks to considerable
support from overseas meteor watchers, most notably those of the
North American Meteor Network, NAMN ( http://www.namnmeteors.org ),
results provided almost immediately after the event by NAMN leader
Mark Davis, hints of the improving rates during the morning UT hours of
November 17, with ZHRs of 30+ after 10h, were found in the Section's
analysis, along with part of the declining rates on the UT morning of
November 18. Sadly however, the very strongest activity was not visible
for our observers in either Europe or North America at this return.
Though the sky-quality many had to endure was not of the highest order,
magnitude distributions for 161 Leonids and 140 sporadics seen under
better conditions (limiting magnitude at least +5.4, cloud cover less
than 20%) suggested the Leonids may have been somewhat brighter
than normal near the peak, with mean magnitude values corrected to an
ideal sky of +2.2 and +3.4 respectively. The sporadic value was much
as expected. Too few train reports were received to analyse those, but
some excellent Leonid trains lasting from tens of seconds up to ten
minutes (and imaged in the latter instance, as mentioned last time)
were noted.
The contributing observers were as follows, including those who
reported casual data via the SPA and UK Weather World Forums (see
http://snipurl.com/tkkl2 and http://snipurl.com/tkkla respectively for more
details on those), where "I" means still-imaging, "R" radio and "V"
visual results were made by that individual:
Salvador Aguirre (Mexico; NAMN; V), "akkan" (England; V), Michael
Boschat (Nova Scotia, Canada; NAMN; V), Mark Davis (South
Carolina, USA; NAMN; V), David Entwistle (England; R + V), Bill
Godley (Oklahoma, USA; NAMN; V), Bill Haddon (California, USA;
NAMN; V), Alan Heath (England; R), Carl Hergenrother (Arizona, USA;
NAMN; V), Ken Hodonsky (Oklahoma, USA; NAMN; V), Mike Linnolt
(Hawaii, USA; NAMN; V), Andy Mayhew (England; I + V), "markh"
(England; I), Alastair McBeath (England; V), Martin McKenna (Northern
Ireland; I + V), Jane Mills (England; V), "OkarcheDave" (Oklahoma,
USA: V), Matthew Phipps (England; V), Richard Taibi (Maryland, USA;
V), William Watson (New York, USA; NAMN; V).
Very many thanks go to all involved so far. Anyone with Leonid data still
to submit, please do so as soon as possible!
NOVEMBER 21-22 IMAGED FIREBALLS
By Alastair McBeath, SPA Meteor Section Director
Two notable fireballs have been reported to the SPA from November
21-22, both of which were imaged. The first was at around 21:00 UT,
seen from numerous places in the Gauteng region of South Africa,
including Johannesburg and Pretoria. It was a brilliant, detonating event,
and was caught on CCTV by-chance. There are links to the video and
media reports via the UK Weather World's Space Weather Forum topic
here: http://snipurl.com/tkm5f .
The second was much closer to home, imaged by automated cameras
run by Armagh Observatory in Northern Ireland. This event was
estimated as brighter than magnitude -5, and happened at 00:57 UT.
Two UK radio meteor observers, Andy Smith in Devon and Richard
White in Northern Ireland, recorded near-simultaneous strong,
protracted echoes beginning at this time, which were likely produced
by the meteor. The Armagh website has more information on their
imaging of the fireball, at: http://snipurl.com/tkmin , while the video is
available here:http://snipurl.com/tkmit . Especial thanks go to Assistant
Meteor Director David Entwistle for rounding-up the information on this
meteor.
Any fresh observations of the "Armagh" fireball, or any others (a fireball
is any meteor of magnitude -3 or brighter), made from the British Isles
or nearby, would be welcomed by the Section. The minimum details I
need from you are:
1) Exactly where you were (give the name of the nearest town or large
village and county if in Britain, or your geographic latitude and longitude
if elsewhere in the world);
2) The date and timing of the event; and
3) Where the fireball started and ended in the sky, as accurately as
possible, or where the first and last points you could see of the trail
were if you did not see the whole flight.
More advice and a fuller set of details to send (including an e-mail
report form) are given on the "Making and Reporting Fireball
Observations" page of the SPA website, at: http://snipurl.com/tkklk .
Good luck to all for the Geminids!
MERCURY MISSION CLEARS HURDLE
BBC News
The European Space Agency (ESA) has approved greatly increased expense
for a mission to Mercury. BepiColombo, due for launch in 2014, was
supposed to cost ESA £595m, but the challenge of building a probe able
to survive the torrid heat and radiation it would suffer has pushed
the price up to £950m. It will be baked directly by the Sun,
receiving some 14,000 watts per square metre, about 10 times what a
spacecraft in orbit around the Earth receives. Developing systems that
that can cope with such an environment has led to the mission getting
heavier. Overall, the launch mass has grown from some three tons to
just over four tons, necessitating a larger, more expensive rocket --
an Ariane-5 instead of a Soyuz.
BepiColombo is a joint endeavour with the Japanese. Two probes will
travel to Mercury, and separate when they achieve orbit (in 2020).
Europe will produce a Mercury Planetary Orbiter which will be equipped
with 11 scientific instruments. Flying in a polar orbit, it will
study Mercury for at least a year, imaging the planet's surface,
generating height profiles, and collecting data on Mercury's
composition and wispy atmosphere. Japan will be responsible for the
Mercury Magnetospheric Orbiter. It will investigate the planet's
magnetic field with its five on- board instruments.
JUPITER SATELLITE NAMED
IAU
The IAU has announced that the 50th confirmed satellite of Jupiter,
S/2003 J 17, is to be named Herse.
V445 PUPPIS MAY BE A TYPE-1a SUPERNOVA PROGENITOR
ESO
The double-star system V445 Puppis is a candidate to become one of the
exploding stars known as Type Ia supernovae. V445 Puppis is the
first, and so far only, nova showing no evidence at all for hydrogen.
It provides the first evidence for an outburst on the surface of a
white dwarf dominated by helium. That is suggestive, as we know that
Type Ia supernovae lack hydrogen and the companion star in V445 Pup
also lacks hydrogen, instead dumping mainly helium onto the white
dwarf. In November 2000, the system underwent a nova outburst,
becoming 250 times brighter than before and ejecting a large quantity
of matter into space.
A supernova is one way that a star can end its life. One sort is
called Type Ia. A defining characteristic of Type Ia supernovae is
lack of hydrogen -- yet hydrogen is the most abundant element in the
Universe. Such supernovae most probably arise in systems composed of
two stars, one of which is a white dwarf. The white dwarf in such a
system can accumulate on its surface matter lost by its companion, but
usually only to a small extent before a surface explosion, that we see
as a nova outburst, occurs and ejects much, perhaps all, of the
accumulated matter back into space.
Astronomers have used an adaptive-optics instrument on the VLT to
obtain images of V445 Puppis over a time span of two years. The
images show a bipolar shell, initially with a very narrow waist, with
lobes on each side. The shell -- unlike any previously observed for a
nova -- is expanding at about 7000 km/s. A thick disc of dust, which
must have been produced during the outburst, obscures the two central
stars. Combining the images with data obtained with other telescopes,
the astronomers determined the distance of the system, about 25,000
light-years, and its intrinsic brightness, over 10,000 times brighter
than the Sun. That implies that the white dwarf has a high mass that
is near its fatal limit and is still being fed by its companion at a
high rate. Whether V445 Puppis will eventually explode as a
supernova, or whether the recent nova outburst has pre-empted that
pathway by ejecting too much matter back into space, is unknown.
SPITZER TELESCOPE OBSERVES YOUNG BROWN DWARFS
JPL
The Spitzer infrared space telescope has contributed to the discovery
of the youngest brown dwarfs ever observed. Brown dwarfs are less
massive and cooler than stars, but more massive (and normally warmer)
than planets. They are often called 'failed' stars, because they lack
the mass necessary to compress their cores to the point where they are
hot enough to ignite the nuclear fusion that burns hydrogen into
helium and powers most stars. They end up as cooler, less-luminous
objects that are difficult to detect. Moreover, young brown dwarfs
evolve rapidly, making it difficult to catch them when they are first
born. In fact, none has been seen in the earliest stages of formation
until now. Now, Spitzer's infrared camera has penetrated a dusty dark
cloud called Barnard 213, a region of the Taurus--Auriga interstellar-
cloud complex well known to astronomers as a hunting ground for young
objects, to observe not one but two of what seem likely to be the
faintest and coolest brown dwarfs ever observed. Observations with
other telescopes have helped to show that the two objects are still
inside the dusty envelope within which they formed.
DARK GALAXY COLLIDING WITH THE MILKY WAY
New Scientist
The Milky Way's neighbourhood may encompass many invisible galaxies,
one of which appears to be colliding with our own. In 2008, a cloud of
hydrogen with a mass then estimated at about 1 million Suns was found
to be colliding with our galaxy. Now it appears that the object is
massive enough to be a galaxy itself. Called Smith's Cloud, it has
managed to avoid disintegrating during its collision with our own,
much bigger galaxy. Furthermore, its trajectory suggests that it
passed through the disc of our galaxy once before, about 70 million
years ago. To have survived, it must contain much more matter than
previously thought, in order to provide enough gravity to hold itself
together. Calculations indicate that it has about 100 times the
previously estimated mass. Simulations of galaxy formation suggest
that a galaxy the size of the Milky Way should be accompanied by about
1000 dwarf galaxies, but only a few dozen have been found so far.
Some of the dwarfs which are (according to the simulation) missing may
be dark galaxies that are all-but invisible.
VESTIGE OF MILKY WAY'S BUILDING BLOCKS?
ESO
The galactic bulge is a troublesome region of our galaxy for
astronomical observations: only infrared light can penetrate its dust
clouds and reveal its myriads of stars. Observations made with the
VLT have shown an unusual mix of stars in a stellar grouping within
the bulge, known as Terzan 5. It appears that that object, unlike all
but a few exceptional globular clusters, does not consist of stars
that were all born at the same time, but formed in at least two
different episodes, about 12 billion and 6 billion years ago. Only
one globular cluster with a similar complex history of star formation
has been observed in the halo of the Milky Way, and that is Omega
Centauri. The new observations show that Terzan 5 is more massive
than previously thought: along with the complex composition and
troubled star-formation history of the system, that suggests that it
might be the surviving remnant of a disrupted proto-galaxy, which
merged with the Milky Way during its very early stages and thus
contributed to the formation of the galactic bulge.
UNIVERSE MAY BE PEPPERED WITH BLUE DWARF GALAXIES
Topix
Astronomers have discovered that the Universe is peppered with tiny
blue dwarf galaxies known as 'blue fuzzies'. The 'tiny' galaxies are
made up mostly of young hot stars that shine brightly, dominating the
light from the galaxies concerned. The discovery was made by
astronomers at the Anglo-Australian Observatory while examining data
from the 'Galaxy and Mass Assembly' survey (GAMA). The aim of the
survey is to map the structure in our local Universe much better than
previous surveys. It incorporates data from the Sloan Digital Sky
Survey, which contains more than 930,000 galaxies and 120,000 quasars,
and extends to approximately 2.5 billion light-years away. When the
astronomers obtained more detailed observations of one of the blue
fuzzies imaged by the survey, they was surprised to discover that it
was in fact an entire galaxy. Since that first discovery, the team
has examined about a hundred more blue fuzzies. The discovery
suggests that the 'nearby' Universe is not dominated by big galaxies
such as the Milky Way or Andromeda, but by lots of small ones.
The blue fuzzies are about the same size as the Small Magellanic
Cloud, averaging around 7000 light-years across and containing as much
mass as seven billion Suns. They are old galaxies, but unlike Milky-
Way-sized galaxies that form stars very rapidly, the blue fuzzies have
their stars forming at a slow but steady pace, giving them a frosting
of young hot stars. They are scattered fairly evenly throughout the
Universe at distances ranging out to seven hundred million light
years. While their distribution follows the voids and filaments which
make up the structure of the cosmos, they seem to be more common in
less-dense areas, away from the large galaxies and galaxy clusters.
Bulletin compiled by Clive Down
(c) 2009 the Society for Popular Astronomy
--
Good Clear Skies
--
Astrocomet
--
Colin James Watling
--
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
--
Web: http://lyra.freewebsites.com/
Good Clear Skies
--
Astrocomet
--
Colin James Watling
--
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
--
Web: http://lyra.freewebsites.com/
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