SPA ENB No. 316

 

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                 The SOCIETY for POPULAR ASTRONOMY

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         Electronic News Bulletin No. 316  2011 September 11

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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/

  

ICE, AND PROBABLY METHANE, ON DISTANT DWARF PLANET

California Institute of Technology

 

Dwarf planet 2007 OR10 orbits the Sun far out in the Solar System and

is about half the size of Pluto, making it the fifth-largest dwarf

planet.  It is one of the reddest objects in the Solar System.  There

are a few other distant dwarf planets that also are red; they are

themselves part of the large group of icy bodies called Kuiper Belt

Objects (KBOs).  The spectrum of 2007 OR10 shows that the surface is

covered in water ice -- a surprise, because although ice is common in

the outer Solar System, it is almost always white, not red.

 

There is, however, one other dwarf planet that is both red and covered

with water ice: Quaoar, which was discovered in 2002 and is slightly

smaller than 2007 OR10.  Quaoar is big enough to have had an

atmosphere and a surface covered with volcanoes that spewed an icy

slush, which then froze solid as it flowed over the surface.  But

because Quaoar is not as big as dwarf planets like Pluto or Eris, it

could not hold onto volatile compounds like methane, carbon monoxide,

or nitrogen as long.  A couple of billion years after Quaoar formed,

it began to lose its atmosphere to space; now, all that remains is

some methane.  Over time, exposure to the radiation from space turned

that methane -- which consists of a carbon atom bonded to four

hydrogen atoms -- into long hydrocarbon chains, which look red.  The

irradiated methane sits on Quaoar's icy surface like frost, giving it

a rosy hue.  The spectrum of 2007 OR10 looks similar to Quaoar's,

suggesting that what happened on Quaoar also happened on 2007 OR10.

Although the latter's spectrum clearly shows the presence of water

ice, the evidence for methane is not definitive at present.

 

 

COLDEST STARS DISCOVERED

NASA

 

Scientists using the Wide-field Infrared Survey Explorer (WISE) have

discovered six 'Y dwarfs' -- star-like bodies with temperatures as

cool as the human body -- all within a distance of about 40 light-

years.  They are the coldest members of the brown-dwarf family,

objects that are sometimes referred to as 'failed stars' because they

are too low in mass to fuse atoms at their cores; instead, these

objects cool and fade with time, until what little light they do emit

is at infrared wavelengths.  Brown dwarfs have atmospheres that are

similar to those of gas giant planets like Jupiter, but they are

easier to observe because they are alone in space, away from the

relatively blinding light of a parent star.  The coldest of the six

Y dwarfs, called WISE 1828+2650, has an estimated atmospheric

temperature less than 25°C.  Another, WISE 1541-2250, is about nine

light-years away and may become recognized as the seventh-closest

star system, in place of Ross 154.

 

EXTREMELY METAL-POOR STAR

ESO

 

A faint star called SDSS J102915+172927, in the constellation Leo, has

been found to have the smallest abundance of elements heavier than

helium of all stars yet studied.  It has a mass less than that of the

Sun and is probably more than 13 billion years old.  Observers at the

VLT found that the proportion of metals in the SDSS star is more than

20,000 times smaller than in the Sun.  It is believed that the

lightest chemical elements -- hydrogen and helium -- were created

at the Big Bang, together with some lithium, while almost all other

elements were formed later in stars.  Supernova explosions spread the

stellar material into the interstellar medium, making it richer in

metals.  New stars formed from the enriched medium, so they had more

metals in their composition than the older stars.  The abundance of

metals is therefore a guide to the age of a star, so the SDSS object

could be one of the oldest stars ever found.  It has a surprising lack

of lithium.  It 'should' have a composition similar to that of the

Universe shortly after the Big Bang, with a few more metals in it.

But the proportion of lithium seems to be at least fifty times less

than expected in the material produced by the Big Bang.  The same

observers have identified several more candidate stars that may prove

to have metal levels similar to, or even lower than, those in SDSS

J102915+172927.

 

UNIFORMITY OF SUPERNOVAE INVESTIGATED

ScienceDaily

 

Type Ia supernovae are thought to occur when a white dwarf in a binary

star system receives additional material from its companion star,

until its mass exceeds a certain limit at which the star initially

collapses but then explodes.  There has recently been interest in

determining the nature of the mass 'donors', with the ultimate goal of

establishing whether supernovae everywhere evolve in the same manner,

having the same luminosity at various stages.  Estimating cosmological

distances depends largely on assumptions about the constancy of the

candle-power of such very luminous objects as supernovae, and the

assumptions need to be tested.  The research has indicated that in

about a quarter of the cases in spiral galaxies, and possibly more,

the companion star that donates mass to the white dwarf is probably an

ordinary medium-sized star, largely similar to the Sun.  [This item is

silent as to the nature of the other three-quarters of the cases, even

in spiral galaxies.]

 

GALAXY WITH EPISODIC JETS

RAS

 

Certain galaxies exhibit jets that are shot out at nearly the speed

of light from the poles of discs of material that is thought to be

rotating round super-massive black holes at the galaxies' cores.

There is one spiral galaxy, nicknamed Speca, that shows evidence for

three distinct episodes of such activity.  It is about 1.7 billion

light-years away, and there are 60-odd other galaxies in a cluster

with it.  They may provide an analogy with what young galaxies and

clusters looked like when the Universe was much younger.  Galaxies in

such clusters would have been gathering up additional material,

colliding with each other, undergoing bursts of star formation, and

interacting with primordial material falling into the cluster from

outside; Speca is showing evidence for many of those phenomena.

 

Speca (an acronym) first came to light in an image that combined data

from the visible-light Sloan Digital Sky Survey with a survey from the

VLA radio telescope.  Images from various radio telescopes operating

at different wavelengths identified three separate pairs of radio-

emitting lobes, providing evidence for three distinct epochs of jet

activity.  The outermost lobes are old enough that their particles

should have lost most of their energy and ceased to produce radio

emission.  It is thought that those old, relic lobes have been

're-lit' by shock waves from rapidly-moving material falling into the

cluster of galaxies as the cluster continues to accrete matter.

 

PROPERTIES OF YOUNG GALAXIES

RAS

 

Scientists have discovered a distant galaxy that throws light on two

fundamental questions of galaxy formation -- how galaxies accrete

matter and how they give off energetic radiation.  It is believed

that, during the epoch when the first galaxies formed, their

ultraviolet light ionized surrounding neutral hydrogen atoms, i.e. it

stripped them of their electrons.  That was the origin of the ionized

plasma that today fills the Universe.  But there is a question as to

how the high-energy radiation was able to escape from the immediate

surroundings of a galaxy, known as the galactic halo.  The galaxies we

observe today tend to be completely surrounded by haloes of neutral

hydrogen, which absorb all the light capable of ionizing hydrogen

before it has a chance to escape into inter-galactic space.

 

The scientists, using the Magellan telescopes at Las Campanas and

archival images from the Hubble telescope, discovered a galaxy with an

extended patch of light surrounding it.  It appeared that roughly half

of the galaxy's radiation must be escaping and exciting hydrogen atoms

beyond its halo.  The key to the escape of radiation was found in the

unusual, distorted shape of the galaxy.  It appears that the object

had recently collided with another galaxy, creating a hole in its

halo, allowing radiation to pass through.  The escape of radiation

during such galactic interactions and collisions may be able to account

for the re-ionization of the Universe.  At early times, when the

Universe was much denser, collisions between galaxies would have been

much more common than they are today.

 

The new observation also demonstrates the flow of in-bound matter, from

which a galaxy initially forms.  In the present case, the escaping

ionizing radiation illuminates a long train of incoming gas, which is

feeding new matter into the galaxy.  The existence of such structures

had been suggested by theory, but they had not been seen previously

because they barely emit any light of their own.

 

 

PLUTO PROBE ON TRACK

NASA

 

One of the fastest spacecraft ever launched -- New Horizons -- is

heading for Pluto.  Launched in 2006, it has been going for longer

than some missions last, and still has four more years to go.  When it

reaches Pluto in 2015 it will have travelled for longer than any

spacecraft has previously flown to reach its main target, although

Voyager 2 had been going for more than 12 years when it had its final

and very successful rendezvous with Neptune in 1989.  To save power

and reduce wear, New Horizons hibernates much of the time.  The probe

is equipped with spectrometers and one of the largest and highest-

resolution interplanetary telescopes ever flown, called LORRI, short

for Long-Range Reconnaissance Imager.  At closest approach to Pluto,

about 10,000 km, LORRI should resolve details almost as well as a spy

camera.

 

 

PLAN TO REVIVE 1970s UK SATELLITE

BBC News

 

When the Prospero spacecraft was launched by a Black Arrow rocket on

1971 October 28, it marked the end of a very short era -- it was the

first UK satellite to be launched on a UK launch vehicle, and it would

also be the last, as Ministers had cancelled the rocket project in the

run-up to the flight.  However, as the Black Arrow was ready, the

programme team decided to fire it anyway.  Prospero was successfully

put into orbit from the remote Woomera base in the Australian desert,

and the satellite is still up there.

 

Carrying a series of experiments to investigate the effects of the

space environment, the satellite operated satisfactorily until 1973

and was contacted annually until 1996.  Now, scientists are hoping

to re-establish communications in time for the satellite's 40th

anniversary.  First, they have to re-engineer the 'ground segment',

but that is not easy because the satellite was built by the Space

Department at the Royal Aircraft Establishment in Farnborough and the

department was broken up long ago.  The codes to contact Prospero were

missing, and the technical reports made in the 1970s were also thought

to have been lost.  The codes were eventually discovered typed on a

piece of paper in the National Archives at Kew.  But even with the

codes, the engineers still have to build equipment to communicate with

the satellite, and to obtain approval from the broadcast regulator

Ofcom to use Prospero's radio frequencies, which are being employed

these days by other satellite operators.  Once that ground segment is

complete, then they will see if it is still possible to communicate

with Prospero.  If the satellite is still alive, some of the

experiments might even be working.

 

 

SPA SOLAR SECTION 2011 AUGUST

By Richard Bailey, Solar Section Director

Rotations Nos. 2113, 2114

 

WHITE LIGHT

 

AR activity in the NH was about four times that in the SH and the

number of sunspots about seven times.  The larger sizes of many NH

ARs also had an effect on sunspot numbers.

 

Week 1:  A line of 3 sizeable NH ARs, 1260, 61 and 63 plus small

1265 near the W limb showed well, the leading AR just past the CM

on the 1st.  By the 7th, ARs 1261 and 63 were by the W limb and

small SH AR1269 by the CM.

Week 2:  A much quieter Sun, only small NH AR 1266, 1270 and SH

AR 1269 were noted.

Week 3:  The 15th had a blank disc.  On the 16th NH AR1271 had

appeared at the E limb and was to develop into a good cluster of

spots during the week, 12 being seen on the 17th. when small SH

AR 1272 was seen by the E limb.

Week 4:  NH AR 1271 continued to grow as it passed the CM, 17

spots being counted including a good leader and follower with

penumbra.  Small NH AR 1274 and SH 1272 and 75 showed on the

22nd. 1271 was at the W limb on the 27th, and two single spots with

penumbra, close together, ARs 1277 and 79, had rotated into view in

the E.  By the end of the month they had moved near the CM.  By

then other small ARs had appeared  to give 5 across the disc.

 

Section members observed  faculae regularly.

 

MDF     2.48               R   37.52

 

H-ALPHA

 

The highlight of the month was the strongest (X7 rated) flare of Solar

Cycle 24 so far, on the 10th, at about 0800 UT.  The large, brilliant

flare appeared in NH AR 1263, then near the W limb.  It was easily

seen through passing clouds and was at its brightest at 0825, but had

faded by 0905.  Prominences again were regularly seen, many large with

complex and ever-changing shapes sometimes across days.  Lengthy

filaments were also often seen, some lasting days, and bright plaging

to ARs.  Some splendid prominences were seen on the S, N and W limbs

on the 15th, a huge W arch dominating, and on the 29th. a large bright

hedgerow one on the E limb.

 

MDF    4.69

 

EXPLANATION OF TERMINOLOGY

('Cut out and keep' this piece if you hope to understand future

Solar-Section reports)

 

For fuller details see Section member Lee Macdonald's book, 'How

to Observe the Sun Safely'; it is available from the SPA Bookshop.

Another excellent guide to Solar Observing,by a former Solar Section

Director, John Chapman-Smith, can be seen on the Solar Section link

from the SPA website.

 

 

White Light Observations of the Sun's surface as normally seen.

 

H-Alpha Observations made through special filters that pass only the

6563-Angstrom wavelength of neutral hydrogen, allowing prominences,

plages, filaments and flares to be seen.  Filaments are prominences

(which stand out from the limb of the Sun) seen against the Sun's disc.

Plages are bright regions often seen where sunspots occur. Flares are

sudden, very bright and often short-lived bursts of energy and matter,

where ARs are seen.

 

NH, SH northern hemisphere, southern hemisphere.

 

CM Central Meridian, the centre line of the Sun's disc between the N

and S poles.

 

AR Active Regions on the Sun where sunspots are seen.  Each is

given a number in sequence as they appear.

 

MDF Mean Daily Frequency of active regions and prominences

reported by Section members.

 

R Mean Daily number of sunspots counted by Section members.

 

Umbra, Penumbra Dark central area of sunspots; paler surrounding

area.

 

Faculae Regions brighter than the normal photosphere (surface of the

Sun), often where sunspots have appeared, or will appear.

 

 

 

Bulletin compiled by Clive Down

 

 

(c) 2011 the Society for Popular Astronomy

 

 

  web site:    http://www.popastro.com/

 

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Good Clear Skies
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Astrocomet
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Colin James Watling

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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)
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