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Дата: 01 апреля 1998 (1998-04-01)
От: Alexander Bondugin
Тема: A Bull's Eye For MERLIN and Hubble
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University of Manchester
Nuffield Radio Astronomy Laboratories
Jodrell Bank
Macclesfield
Cheshire SK11 9DL
England
PRESS RELEASE: PR9801 27th March 1998
A Bull's Eye for MERLIN and the Hubble
A team of British astronomers using the UK's MERLIN radio array and the
Hubble Space Telescope have found an ``Einstein Ring'' -- a gravitational
effect predicted by Albert Einstein over 60 years ago as a consequence of
his General Theory of Relativity. The Hubble picture is a beautiful
demonstration of Einstein's ideas since, for the first time, it shows a
complete ring surrounding the galaxy that created it.
The effect is a cosmic mirage caused by the gravity of a massive galaxy
bending the light from an object behind it and acting as a ``gravitational
lens''. On the rare occasions when the distant object, the lens galaxy and
the telescope are exactly aligned an ``Einstein ring'' is created.
Dr. Ian Browne of the University of Manchester admits ``At first sight
it looks artificial and we thought it was some sort of defect in the
image but then we realised we were actually looking at a perfect
Einstein ring!''.
Commenting later on the pictures Bristol University astronomer Professor
Mark Birkinshaw said ``MERLIN and the Hubble have scored a bulls-eye!''.
The size of the ring on the sky is tiny -- roughly a second of arc or about
the size of a penny viewed from a distance of over two miles -- even though
the lens consists of an entire galaxy. The blurring effect of the atmosphere
makes such fine detail hard for astronomers to spot using optical telescopes
on the Earth.
The British team found it by using the 135 mile-wide MERLIN radio telescope
to image distant radio sources. MERLIN is a network of six radio telescopes
spread out across England and operated as a national facility by the
University of Manchester's Jodrell Bank observatory. MERLIN's resolution is
the same as that of the Hubble Space Telescope but at a completely different
wavelength -- the two make perfect astronomical partners. The Hubble,
orbiting above the atmosphere, took a detailed picture of the object and
this revealed the spectacular bulls-eye. This is only one of over 20 galaxy
lenses now known.
In an ironic twist, counting the number of gravitational lenses in the sky,
including the rare Einstein rings, is the best way of seeing whether
Einstein really made his ``greatest blunder''. When he applied his General
Theory of Relativity to the Universe as it was known 80 years ago, Einstein
had to invent a repulsive force which overcomes gravity at very large
distances. This new force was soon dismissed by other astronomers but many
modern cosmologists now think that Einstein may have been right first time --
the lens searches will soon tell us where the truth lies.
Background information on gravitational lenses is available by clicking
HERE. [http://www.jb.man.ac.uk/merlin/press/PR9801/press2.html]
The results of this work will be published in Letters section of the April 1
Issue of the Monthly Notices of the Royal Astronomical Society.
L.J. King et al. ``A complete infrared Einstein ring in the
gravitational lens sytem B1938+666''
The MERLIN radio array is a UK National Facility operated by the University
of Manchester on behalf of the Particle Physics and Astronomy Research
Council. The Very Large Array is a US National Facility operated by the
National Radio Astronomy Observatory on behalf of Associcated Universities
Inc.
The astronomers involved work at the following institutes: University of
Manchester; University of Oxford; California Institute of Technology
(Pasadena); Netherlands Foundation for Radio Astronomy; University of
Groningen; Institut d'Astrophysique de Paris.
For further information contact any of the following team members:
The following may be contacted at Jodrell Bank, at
Telephone: 01477 571321
FAX: 01477 571618
Address: Nuffield Radio Astronomy Laboratories
Jodrell Bank
Macclesfield
Cheshire SK11 9DL
* Dr. Neal Jackson, Lecturer, Dept. of Physics and Astronomy, Univ.
Manchester
Email: njj@jb.man.ac.uk
* Dr. Peter Wilkinson, Acting Director, MERLIN/VLBI National Facility
Email: pnw@jb.man.ac.uk
NOTE: During the period Tuesday 31 March to Friday 3 April Dr.
Wilkinson will be attending the UK National Astronomy Meeting (NAM) at
the University of St. Andrews.
He can be contacted at via the NAM press room, whose hours are:
Tuesday to Thursday, 8.30 - 18.00, and 9.00 - 12.00 Friday.
Telephone: 01334-462168 and 462169
FAX: 01334-463130
PHOTO CAPTION:
Figure 1 [http://www.jb.man.ac.uk/merlin/press/PR9801/picture1.html]
Hubble and MERLIN image of 1938+666. A postscript version is available
for Figure 1.
(Upper) The Hubble Space Telescope picture of the distant galaxy 1938+666
which has been imaged into an Einstein ring by an intervening galaxy. The
intervening galaxy shows up as the bright spot in the centre of the ring.
The picture was taken in the infra-red region of the spectrum and the
computer-generated colour of the image has been chosen simply for ease of
viewing.
(Lower) The MERLIN radio picture of the radio source 1938+666 embedded in
the distant galaxy. The incomplete ring (or arc) shows that the radio source
is not perfectly aligned with the lens galaxy and the Earth. The lens galaxy
does not contain a radio source and hence does not show up in this picture.
The colours are computer-generated and represent different levels of radio
brightness.
Figure 2 [http://www.jb.man.ac.uk/merlin/press/PR9801/picture2.html]
Diagram demonstrating the principle of a gravitational lens. A postscript
version is available for Figure 2.
Diagram showing the formation of a gravitational lens images. In the upper
diagram the distant object, the lens galaxy and the Earth are perfectly
aligned. The lens galaxy formed a perfect ring-like image known as an
Einstein Ring. In the lower diagram the distant object, the lens galaxy and
the Earth are not perfectly aligned. In this case the lens galaxy forms
multiple images of the distant object.
*****
PRESS RELEASE: PR9801 12th March 1998
A Bull's Eye for MERLIN and the Hubble
Background Information
The observations
Because of the blurring effect of the atmosphere on optical telescopes, the
astronomers use high resolution radio telescopes -- the Very Large Array in
New Mexico and the MERLIN array in the UK (see the main MERLIN WWW page at
http://www.jb.man.ac.uk/merlin/) -- to pick out gravitational lens systems.
Only about one in every five hundred distant radio sources (galaxies and
quasars) is lensed and so thousands of radio sources have to be searched to
have a good chance of success. The British team, working together with an
international team of colleagues, have now found thirteen such systems --
more than doubling the number previously known.
The radio picture produced by MERLIN (Figure 1), which allowed the system to
be recognised in the first place, shows only part of a ring. The reason is
that, while the source of radio emission is embedded in the distant galaxy,
it is not exactly aligned with the lens galaxy. The ``optical'' picture
produced by the Hubble (Figure 1) is actually in the infra-red region of the
spectrum taken with the NICMOS camera. The wavelength used is about twice
that of red light. The infra-red emission from the distant galaxy is more
extended than the radio emission. Some of it comes from directly behind the
lens galaxy and hence a complete ring is formed.
Gravitational Lensing
Unlike the lenses with which we are familiar, in spectacles for example, a
gravitational lens can produce not one but several images of a given object;
these images may be highly distorted and magnified. Whereas a conventional
glass or plastic lens has a simply curved shape the analogy with a
gravitational lens is a piece of glass shaped like the base and stem of a
wine glass with the bowl cut off. Even without breaking the glass the ring
effect can easily be seen by tipping the glass and looking at a mark on a
piece of paper (or a table cloth) through the base.
The way in which a gravitional lens produces multiple images, including the
special Einstein ring case, is illustrated in the explanatory diagram
(Figure 2).
Why study gravitational lenses?
By studying this and other gravitational lenses astronomers can not only
measure the masses and shapes of distant galaxies, including any ``dark''
matter which will not show up in the optical or radio pictures, but also can
measure Hubble's constant which is related to the time elapsed since the Big
Bang.
Einstein's ``greatest blunder'' refers to the elusive Cosmological Constant.
This describes the strength of the long-range repulsive force he introduced
into the General Relativity equations in 1916. Other astronomers soon
showed, however, that this force was not needed to explain the properties of
the Universe as it was then known. Einstein ruefully wrote ``away with the
cosmological term''. But like a genie, once released it has proved hard to
put away and many astronomers now invoke the Cosmological Constant to
account for modern observations of the distant universe.
A Universe in which the Cosmological Constant is not identically zero has
different geometrical properties to one governed solely by gravity. Counting
gravitational lenses, in other words counting the number of lines-of-sight
``blocked'' by intervening galaxies, is acknowledged to be the best way of
measuring the geometry of the Universe at large distances. By the end of
this year we expect to be able to place the best limit so far on the
Cosmological Constant.
Hа сегодня все, пока!
=SANA=
Дата: 01 апреля 1998 (1998-04-01)
От: Alexander Bondugin
Тема: A New View Of Mass Ejections: Watching The Sun Cough
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Royal Astronomical Society Press Notices
Date: 27 March 1998
Ref. PN 98/08 (NAM5)
Issued by:
Dr Jacqueline Mitton
RAS Public Relations Officer
Phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@ast.cam.ac.uk
and
Peter Bond
Space Science Advisor
Phone: (0)1483-268672
Fax: (0)1483-274047
E-mail: 100604.1111@compuserve.com
A NEW VIEW OF MASS EJECTIONS: WATCHING THE SUN COUGH
It seems that the behaviour of the Sun in some ways resembles that of humans
with a dry throat: the first spasm leads to a further series of coughs in a
kind of chain reaction. In the case of the Sun, huge clouds of hot gas are
ejected during each spasm in the form of Coronal Mass Ejections. This, and
other new results from the LASCO (Large Angle Spectrometric Coronagraph)
instrument on board the European Space Agency/NASA spacecraft SOHO (Solar
and Heliospheric Observatory), will be presented at the UK National
Astronomy Meeting at the University of St Andrews by Dr Mark Lyons from the
University of Birmingham.
What Are CMEs?
Astronomers have known since the early 1970s that Coronal Mass Ejections
(CMEs) are regularly thrown out into space by the Sun. These huge clouds of
gas consist of electrically charged particles (protons and electrons) and
have a typical mass of hundreds of millions of tonnes. In some cases they
are directed towards the Earth and they travel so rapidly that they usually
cross the 150 million km gap within three days of their launch from the Sun.
Scientists would very much like to be able to forecast these events since,
on arrival, they interact with the Earth's magnetic field, producing
geomagnetic disturbances which can disrupt electricity supplies and cause
damage to satellites.
In addition, understanding how CMEs are produced is crucial to understanding
the overall workings of the Sun. They are a dominant feature of the solar
corona (the white halo seen around the Sun during solar eclipses) and may
play a major role in the behaviour of the solar magnetic field.
LASCO
The latest tool being used to advance the research into CMEs is the LASCO
instrument carried on board the SOHO satellite. LASCO is a joint project
between the University of Birmingham, the Naval Research Laboratory
(Washington DC), the Max-Planck-Institut fur Aeronomie (Germany) and the
Laboratoire d'Astronomie Spatiale (France). It consists of three telescopes
(known as coronagraphs) which are capable of blocking out the bright disk of
the Sun and allowing the fainter light from the corona to be observed.
Combined, the three coronagraphs of LASCO give images of the solar corona
from 1.1 to 30 solar radii (from just above the visible surface to a
distance of about 20 million km from the Sun). This wide angle view and its
high sensitivity give LASCO a tremendous advantage over previous
instruments.
In general, a CME is thought to occur when closed magnetic configurations in
the solar corona are destabilised by some trigger. This destabilisation then
leads to the expulsion of matter from the solar atmosphere. The latest
research at Birmingham is revealing that the entire Sun can be affected by
CMEs. This is displayed most strikingly by events observed by LASCO where an
initial mass ejection is closely followed by a series of others. In some
cases CMEs occur at widely separated points almost simultaneously. For the
first time LASCO is showing us that the corona behaves as a single unit,
capable of storing large amounts of magnetic energy which can be released
from more than one point by some initial triggering mechanism.
Further evidence for a global reaction of the corona was provided by an
event observed on the 23rd February 1997. LASCO C1 images (covering a region
from 1.1 to 3 solar radii) showed the expansion of a CME in the lower corona
moving with a speed of 880 km/s from the north-east limb of the Sun. This
quickly destabilised a sequence of much larger magnetic loop structures to
the south which then became the dominant feature of the CME. This sequence
of events implies that a higher magnetic loop system spans the solar equator
to physically connect regions in opposite hemispheres.
The Solar Wind
For a long time the Sun has been known to produce a 'wind' of charged
particles. Mass ejections from the Sun are known to contribute a significant
fraction of the total material of solar wind. LASCO observations are now
providing new information about the flow of the solar wind nearer to solar
surface where its properties have not been closely studied.
A study of CME events carried out by Professor George Simnett at Birmingham
University has shown that they begin to undergo an acceleration at a
distance of about 6 solar radii. So the LASCO observations indicate that
this is probably where the solar wind begins.
Notes for Editors
The SOHO satellite was launched in December 1995. It orbits a stable point
(the Lagrangian L1 point), situated approximately 1.5 million km from Earth
towards the Sun at which the gravitational pull on the satellite from the
Earth and the Sun are equal. This position ensures that LASCO has an
uninterrupted view of the Sun.
LASCO observations will continue as solar activity moves towards a maximum
in its 11 year cycle by the end of the century. Dr Mark Lyons is a research
fellow working on the LASCO project at the University of Birmingham. The
solar group at the University of Birmingham, headed by Prof. George Simnett,
is using images from LASCO to provide new insights into the CME process.
More information about the LASCO research carried out by the solar group at
the University of Birmingham and about the SOHO project, including images of
CMEs, can be found on the following Web sites.
* http://www/research/solar.html
* http://lasco-www.nrl.navy.mil/lasco.html
Contact
Dr Mark Lyons,
School of Physics and Astronomy,
University of Birmingham, Birmingham B15 2TT.
Tel: +44 (0)121 414-4608
E-mail: mal@star.sr.bham.ac.uk
Press room at the National Astronomy Meeting, University of St Andrews
(8.30 - 18.00 Tue 31 March to Thur 2 April; 9.00 - 12.00 Fri 3 April):
Phone: 01334-462168 and 01334-462169
Fax: 01334-463130
Hа сегодня все, пока!
=SANA=
Дата: 01 апреля 1998 (1998-04-01)
От: Alexander Bondugin
Тема: Hubble Images Of Comet Hyakutake Released
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The University of Michigan
News and Information Services
412 Maynard
Ann Arbor, Michigan 48109-1399
Contact: Adam Marcus
Phone: (734) 647-7046
E-mail: marcusa@umich.edu
News Release: March 27, 1998
Hubble pictures from study of Comet Hyakutake released
EDITORS: A complete description of the results of the program and
the individual images can be accessed via the World Wide Web from
URL http://www.sprl.umich.edu/SPRL/Comets/Hyakutake.html
ANN ARBOR -- University of Michigan astronomer Michael Combi has
released two images of the inner coma, or gassy head, of Comet
Hyakutake, which passed within about 16 million kilometers of Earth
in 1996. The computer-generated pictures were taken with NASA's
Hubble Space Telescope on April 4, 1996, during observations led by
Combi, a research scientist at the U-M College of Engineering.
These images, made using Hubble's Wide Field Planetary Camera 2,
were part of a study of water photochemistry in comets. Hydrogen
atoms are the most abundant gas in the entire coma of the comet.
They are produced when solar ultraviolet light divides molecules of
water, the major constituent of the nucleus of the comet. Using
Hubble's High Resolution Spectrograph, Combi and his colleagues
were able to determine that Hyakutake was churning out between 7
and 8 tons of water per second, by matching a computer model of the
comet the researchers had created earlier to the observations.
"The importance of such a detailed model is that it permits the
accurate calculation of the production rate of water from
observations," Combi said. The results appear in an article in the
Feb. 20, 1998, issue of the Astrophysical Journal (vol 494, pages
816-821).
The first image, shown in red, was taken through a narrow-band red
filter that shows only sunlight scattered by dust particles in the
inner coma of the comet. The second, shown in blue, was taken with
an ultraviolet "Woods" filter image that shows the distribution of
scattered ultraviolet radiation from hydrogen atoms in the inner
coma.
The inner yellow region near the center of the red dust image is
dominated by the contribution from the dust which shows sunward
directed spiral jets toward the upper right, and the thin straight
particle trail pointing toward the lower left. The trail was a
permanent feature of the comet around the time of its close
approach to the earth in late March and early April. Also barely
visible just beyond the lower left end of the trail are two of the
many condensations which were seen to travel slowly down the tail
are believed to be clumps of material released from the comet's
nucleus -- a 2-3 km chunk of dirty ice.
The inner white region of the blue image appears to show that the
hydrogen atoms like the dust might be preferentially ejected toward
the sunward or day side of the nucleus. However, this is not true.
The asymmetric ultraviolet radiation pattern is produced by a
roughly spherical distribution of hydrogen atoms because they are
so efficient at scattering the incoming solar ultraviolet light.
The atoms on the sunward side actually shadow the atoms on the
tailward or night side of the coma. The same detailed model
analysis of the coma which explains the expansion of the hydrogen
atoms in the coma also explains the appearance of the image.
Combi's team included Michael Brown of the California Institute of
Technology, Paul Feldman of the Johns Hopkins University, H. Uwe
Keller of the Max Planck Institute, Lindau, Robert Meier of the
Naval Research Laboratory, and William Smyth of Atmospheric and
Environmental Research, Inc.
[NOTE: Images supporting this release can be accessed directly at
http://www-personal.engin.umich.edu/~mcombi/HST/hyaku.html]
Hа сегодня все, пока!
=SANA=
Дата: 01 апреля 1998 (1998-04-01)
От: Alexander Bondugin
Тема: Hunt Is On For More Extrasolar Planets
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Royal Astronomical Society Press Notices
Date: 30th March 1998
For immediate release
Ref. PN 98/11 (NAM8)
Issued by:
Dr Jacqueline Mitton
RAS Public Relations Officer
Phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@ast.cam.ac.uk
HUNT IS ON FOR MORE EXTRASOLAR PLANETS
The UK National Astronomy Meeting (NAM) at the University of St Andrews
opens on Tuesday 31st March with astronomers expressing high hopes of
finding more extrasolar planets in the near future, and of learning much
more about planetary systems beyond our own, as major new research projects
get under way at the Anglo-Australian Observatory (AAO) in New South Wales,
and at the observatory on La Palma in the Canary Islands.
The Anglo-Australian Planet Search Project
Commenting on the AAO programme, AAO astronomer Chris Tinney said, "This
southern hemisphere program is exciting, because it is the first time the
virgin territory of the southern sky has been searched. Every southern star
we observe is being checked for the first time. And the experience of the
northern hemisphere shows we can expect to find the first new planets within
about a year. Altogether, we hope to double the number of nearby stars with
known planets over the next five years."
The AAO observations form part of an international project to examine nearby
stars similar to the Sun for the presence of planets. The project stems from
the highly successful search by Geoffrey Marcy and Paul Butler at Lick
Observatory in California. Marcy and Butler are the world's leading
discoverers of extrasolar planets with 6 independent finds to their credit.
Because many stars in the far southern sky are not visible from Lick, Paul
Butler will be working on the 3.9-metre Anglo-Australian Telescope at the
AAO in collaboration with Chris Tinney, Hugh Jones (Liverpool John Moores
University) and Alan Penny (Rutherford Appleton Laboratory), who will talk
about the project at the NAM.
The LA Palma Exoplanet Programme
Observations to start in May on La Palma will be described by Professor
Keith Horne of the University of St Andrews, who is a member of a 20-strong
team of astronomers from 15 different institutions, mainly in Europe. He
explains, "We were awarded the 1998 'International Tim
