A FIERY rain in the primeval Solar System may explain why some meteorites
are strange mixtures of minerals that were once melted with others that were
not. Researchers came up with the idea after studying a new, detailed picture of
the formation of stars like the Sun.

Frank Shu of the University of California at Berkeley and his colleagues
suggest that winds ejected from the two poles of the forming Sun—like the
bipolar winds Hubble Space Telescope has spotted around other
protostars—lifted fluffy, heated rocks from near the forming Sun and then
sprayed them all over the Solar System. These chondrules or beads of melted rock
later combined with colder dust to form asteroids and planets, Shu told last
week’s meeting of the American Astronomical Society in Winston-Salem, North
Carolina.

Using a detailed theoretical model of the young Sun’s winds, the researchers
calculate that only chondrules between a millimetre and a centimetre across
would fall back onto the forming planetary system. That is, in fact, the range
of chondrule sizes seen in the most common meteorites, called chondrites.

Shu’s team has also explained the presence of unusual radioactive elements
found in meteorites. They suggest that the young Sun must have generated
energetic magnetic flares, similar to those recently detected by the Japanese
X-ray satellite ASCA from several protostars. The fast-moving protons in those
flares would combine with ordinary elements in the protoplanetary disc to form
their radioactive counterparts, according to the team’s model.

“This is the first theory to explain all the disparate features of
chondrites,” says Shu. Eric Feigelson of Pennsylvania State University,
University Park, agrees that their “basic premise is very persuasive”.

Researchers have found evidence for a high abundance of carbon in the infant
Universe. Since the big bang is believed to have produced only the lightest
elements, such as hydrogen and helium, heavier elements like carbon must have
formed through nuclear reactions within stars. When these exploded as
supernovae, the carbon was spewed out into space.

Now Jordi Miralda-Escude of the University of Pennsylvania in Philadelphia
and Martin Rees of the University of Cambridge have proposed that some primeval
stars of lower mass may still exist in the halo of stars that surrounds our
Galaxy. Such stars do not collapse violently and explode, but burn their fuel
slowly, and so may have survived. They argue that early dwarf galaxies
containing the first stars have merged to form existing galaxies, like our Milky
Way. If so, as many as half the stars in our Galaxy’s halo may be
old-timers.

Richard Larson of Yale University agrees that a very early generation of
stars is needed to account for the heavy elements seen in distant gas clouds.
But he believes that most of those stars were massive and would have
self-destructed as supernovae. Their remnants—black holes and neutron
stars—may, however, still be in the halo of the Galaxy.

Miralda-Escude and Rees have also calculated how many supernovae would be
needed to produce the observed carbon abundance in the early Universe. In a
paper submitted to Astrophysical Journal Letters, they report that a
few hundred such supernovae should be observable at any given time in a patch of
the sky twice as big as that covered by the Moon. But being so distant, these
stars would be extremely faint—in fact, about ten times too faint to be
seen by today’s most powerful telescopes.

There may be another way to detect the effects of early stars. The first
generation of stars must have left an imprint on the cosmic microwave background
radiation, argue Zoltan Haiman and Abraham Loeb of Harvard University in another
paper submitted to the Astrophysical Journal.

Haiman and Loeb predict that two satellite missions to be launched in
1998—one by NASA and the other by the European Space Agency—should
detect that imprint.

THE Sun has a pulse that no one has ever noticed before, according to
astronomers in California. Peter Sturrock and GĂźnther Walther of Stanford
University claim that the number of neutrinos rushing out from the Sun into the
Solar System varies in a regular cycle that peaks every 21.3 days.

Neutrinos, chargeless particles that can pass straight through the Earth, are
produced during nuclear fusion reactions in the Sun’s core. Sturrock and Walther
uncovered a regular cycle in their arrival at the Earth by studying 20 years’ of
data at the Homestake mine in South Dakota, where a huge tank of oil records
neutrinos as flashes of light. They have found the same periodicity after
combining data from two other neutrino detectors: one called Gallex in Italy
and the Kamiokande detector in Japan.

The regular variation in the number of solar neutrinos could mean one of two
things, Sturrock and Walther argue in a paper submitted to Astrophysical
Journal Letters. One possibility is that part of Sun’s core rotates every
21.3 days, and that as neutrinos are on their way out they interact with a
magnetic field embedded in it. If so, neutrinos—which some physicists
think are massless—would have to have mass. Recent experiments with
particle accelerators also imply that neutrinos have mass (New
ĐÓ°ÉÔ­´´, Science, 11 February 1995, p 14). The other possibility is that
nuclear fusion in the solar core is not steady, as is usually assumed, but
cyclic. For this to be the case, different parts of the Sun’s interior must spin
at different rates, creating periodic flows of material into the core.

Douglas Gough, a theorist at Cambridge University, says that Sturrock and
Walther’s finding “suggests something interesting is going on in the solar
core”. But he says it is still possible that the apparent neutrino cycle is a
statistical artefact.

THE discovery of carbon monoxide in the farthest reaches of the Universe has
given astronomers their strongest proof yet that generations of massive stars
had already lived and died within the first billion years after the Universe
began.

In this week’s issue of Nature (vol 382, pp 426 and 428), two teams
of astronomers independently report evidence of carbon monoxide molecules
in the
distant quasar BR1202-0725. The teams, led by Kouji Ohta of Kyoto University in
Japan and Alain Omont of the Institute of Astrophysics in Paris, detected radio
waves emitted by slight distortions in the chemical bond between atoms as
carbon
monoxide molecules spin end over end.

The quasar is one of the most remote objects in the known Universe. Since
looking so far away is the same as looking back in time, astronomers are seeing
the quasar as it was when the Universe was only about 7 per cent of its current
age.

The big bang is believed to have produced only the lightest of
elements, such
as hydrogen and helium. Heavier elements such as carbon, oxygen and
silicon were
formed later, through nuclear reactions within stars, and spewed out into
interstellar space when massive stars exploded as supernovae.

Heavy elements have been seen in two slightly more distant—and hence
earlier—quasars, but no one has been certain that there was more than a
trace present. In order to form detectable amounts of carbon monoxide, however,
there must be “a galaxy’s worth” of these heavier elements, says Richard
Barvainis of the Haystack Observatory in Westford, Massachusetts.

If there was a flurry of star formation in primitive galaxies, as the new
observations imply, this might explain why astronomers see so few distant
quasars. The dust and gas enriched by heavy elements could obscure the visible
light from the stars themselves and hide any quasar shining from within the
galaxy’s nucleus. “Perhaps the reason for the fall off of quasars is not that
they don’t exist in the very early Universe, but that they are obscured by dust
and hard to recognise,” says Barvainis.

A cloud of dust and gas that lies 25 000 light years away contains vinegar,
according to astronomers in the US.

At last week’s meeting of the American Astronomical Society in Madison,
Wisconsin, researchers announced results from the recently dedicated
Berkeley-Illinois-Maryland Association (BIMA) array of radio telescopes near Hat
Creek, California.This array has detected the signature of acetic acid
molecules—better known as vinegar—in spectra from a dense cloud of
gas called Sagittarius B2, located near the centre of our Galaxy.

“Acetic acid could have been one of the first steps toward the chemicals of
life,” says Lewis Snyder of the University of Illinois in Urbana-Champaign, a
member of the discovery team.

Ammonia is already known to exist in interstellar space, and it could combine
with acetic acid to form the simplest amino acid, glycine. Amino acids are the
building blocks of proteins and DNA, and essential ingredients of living
things.

Two years ago, one member of Snyder’s team tentatively reported that he had
found glycine itself in the same region of space (New ĐÓ°ÉÔ­´´, 11
June 1994, p 4). But this has proved difficult to verify.

“The discovery of acetic acid makes it very plausible that amino acids do
exist in space,” says Snyder.

The Solar System may be heading for a dense patch of gas and dust that could
dramatically affect conditions on Earth. Priscilla Frish of the University of
Chicago told participants at last week’s meeting of the American Astronomical
Society in Madison, Wisconsin, that the Sun and its planets could be in for a
bumpy ride—sometime in the next 50 000 years.

For most of the past five million years, the Solar System has been moving
through a rather empty region of interstellar space between the spiral arms of
the Milky Way. But a few thousand years ago, it entered a diffuse shell of
material expanding outward from an active star-forming region called the
Scorpius-Centaurus Association. Such “superbubble” shells of gas and dust result
from the formation of massive stars, or the explosion of those stars as they
become supernovas, and contain gas and dust clouds of varying densities.

The amount of interstellar gas heading towards the Solar System is increasing
as the shell expands. “This cloud, although low density on average, has a
tremendous amount of structure to it,” says Frish, “and the Sun may eventually
encounter a portion of the cloud that is a million times denser than what we’re
in now.”

At present the solar wind, the flow of charged particles that streams away
from the Sun, protects the Earth from direct interaction with interstellar
material by enveloping it and all the other planets in the heliosphere, the
region of the Sun’s influence. But if the heliosphere encountered a much denser
cloud, it could be compressed almost to the size of the Earth’s orbit. “There
would be dramatic effects on the inner Solar System,” says Frish. Astronomers
have suggested that such an encounter could cause changes in the Earth’s
magnetic field, atmosphere and climate.

Other scientists confirmed that the Sun’s immediate neighbourhood is far from
uniform. John Watson and David Meyer of Northwestern University in Evanston,
Illinois, studied the spectra of 17 binary stars. They found that interstellar
space appeared to absorb more of a particular wavelength of light from one star
in a pair than from the other. Since each star in a binary system is the same
distance from Earth, differences in absorption must be due to clumps of gas in
the space between the two stars. They conclude that the Sun’s immediate vicinity
could be littered with dense pockets of gas, roughly the size of the Solar
System.

Researchers led by Jean-Loup Puget of the Institute of Space Astrophysics in
Paris have analysed data from the Far-Infrared Absolute Spectrometer (FIRAS), an
instrument on the Cosmic Background Explorer (COBE) satellite. Dust heated by
stars emits infrared radiation with a wavelength of a few hundred micrometres.
After subtracting emissions from dust in the Milky Way, Puget’s team says that
the remaining radiation looks the same in every direction and has a different
spectrum from emissions of the dust in our Galaxy (Astronomy and
Astrophysics, vol 308, p L5).

The astronomers argue that the uniformity of this far-infrared background
radiation shows it must have originated from incredibly distant objects. Because
peering deep into space is the same as looking back through time, the radiation
must have been emitted when the Universe was in the first flush of youth. “The
far-infrared background could help us better understand early galaxy evolution,”
says Puget.

Not all astronomers are convinced, however. Whether Puget has detected a true
cosmic background depends on the effectiveness of his methods for subtracting
the emissions of nearby dust. Puget assumed that dust in different parts of the
halo that surrounds our Galaxy has the same properties. But if the distribution
of that dust varies, or if dust in different places has very different grain
sizes and temperatures, Puget’s calculations could go awry. “They could very
well have the right answer, but we can’t be sure just yet,” says Richard Shafer
of the NASA Goddard Space Flight Center in Maryland, and a member of the team
that built the FIRAS instrument.

This team is conducting its own search for the far-infrared background, using
more sophisticated models of the distribution of dust in the Galactic halo.

If the far-infrared background is real, there are two possible explanations.
One is that the glow comes from dust in young massive elliptical galaxies,
harbouring hordes of newly formed stars. The spectrum of the emissions described
by Puget’s team suggests that at least some of these galaxies must have formed
when the Universe was only three per cent of its present age—earlier than
most theories allow.

Another explanation is that the dust responsible for the emissions lay in
smaller, distant spiral galaxies similar to the Milky Way, which are believed to
have formed when the Universe was about 10 per cent of its current age.
Astronomers led by Michael Fall of the Space Telescope Science Institute in
Baltimore, Maryland, have calculated how much infrared radiation could be
expected from such distant spiral galaxies, whose presence can only be inferred
from their absorption of light from quasars. In a paper due to appear in
Astrophysical Journal Letters next month, they conclude that these galaxies
could emit enough infrared to account for at least half of the background found
by Puget’s team, and possibly more.

MOST of the ordinary matter in the Universe is invisible. That is the
conclusion of astronomers in the US who have studied a “shadow” cast in space by
a heavy isotope of hydrogen.

The good news is that cosmologists do not have to invoke exotic, undiscovered
particles to account for the Universe’s “dark matter”. The bad news is that it
implies that the cosmos contains more helium and lithium than has been
detected—a discrepancy that creates problems for the big bang theory.

David Tytler and his team at the University of California, San Diego, looked
for the signature of deuterium in the spectrum of a distant quasar. Deuterium is
a form of hydrogen in which each atomic nucleus contains a neutron as well as a
proton. It absorbs light at a specific wavelength and the strength of this
“absorption line” in a quasar’s spectrum reveals the amount of deuterium in gas
clouds between the quasar and us.

Deuterium was formed in the neutron-rich environment instants after the big
bang. Its abundance depends on the density of ordinary matter in this primordial
furnace. The greater the density of matter, the lower the yield of deuterium.
Once astronomers have good measurements of the abundance of deuterium, they can
use the big bang model to predict the abundance of helium and lithium.

The quasar’s spectrum revealed that the clouds contained only two atoms of
deuterium for every 100 000 of hydrogen—ten times less than astronomers
have suggested (Nature, vol 381, p 207). This result implies that 90
per cent of the Universe’s ordinary matter is invisible, perhaps existing as
burnt out stars in galaxy haloes.

The new data also imply that more helium and lithium were forged in the big
bang than astronomers have observed. “It’s a potential crisis for cosmology,”
says Gary Steigman of Ohio State University in Columbus, who studies element
formation in the early Universe. Either the current big bang model is wrong, or
there are problems with the measurements of deuterium or those of lithium and
helium.

Augustus Oemler of Yale University and his colleagues at three other
American institutions have mapped the positions of about 5000 galaxies out
to a distance of 5000 megaparsecs (about 16 billion light years). They are
only halfway through their survey, but the first results show that the matter
in the Universe is distributed homogeneously.

The first concrete evidence for homogeneity in the Universe came in
1965 when Arno Penzias and Robert Wilson of AT & T Bell Labs discovered
the ‘cosmic background radiation’. The radiation, a dim afterglow from the
fireball of the big bang, is remarkably even all over the sky, indicating
that the Universe was a smooth place in the beginning.

But other evidence indicates that the Universe is not smooth at all,
but clumpy. As astronomers have mapped ever larger regions of space, they
have come across bigger and bigger structures, such as clusters and superclusters
of galaxies millions of light years across.

A few years ago, Margaret Geller and John Huchra of the Harvard-Smithsonian
Center for Astrophysics discovered a giant wall of galaxies, bigger than
any known supercluster. This Great Wall extended beyond the 125 megaparsec
limit of the astronomers’ survey, so it had to be even bigger.

To many astronomers, it seemed as if the size of the largest known structure
increased hand in hand with the scale of galaxy surveys. But the new survey
carried out by Oemler and his colleagues may mark the end of this uncomfortable
trend.

The astronomers used telescopes at the Las Campanas Observatory in Chile
to observe fairly large strips of the sky. Although the new survey extends
four times deeper into space than the Geller-Huchra survey, it has turned
up no structure bigger than the Great Wall. And Oemler and his colleagues
are confident that their preliminary findings will soon be strengthened.
They intend to map a further 5000 galaxies over the next two years.

Meanwhile, several other groups are planning their own galaxy surveys.
Paolo Vettolani of the Radio Astronomy Institute in Bologna, Italy, and
his colleagues at the European Southern Observatory in Chile will begin
a survey next year. They hope to map two strips of the sky, each 24 degrees
long and 2 degrees wide.

Another group of astronomers, from the University of Chicago and Princeton
University, has announced a more ambitious plan. They want to map as much
as a quarter of the sky, and measure the distances of a million galaxies.

To carry out this task, the astronomers intend to use a new 2.5-metre
telescope with a wide field of view. The telescope is being built in New
Mexico specially for the project. It should be ready in 1994, when the survey
is expected to start.