Astronomy - June 2015

ASTRONEWS

J0100+

Luminosity (solar luminosity)

10

trillion

(^100) trillion
1
quadrillion
Black hole mass (solar mass)
100
million
1
billion
10
billion
WWW.ASTRONOMY.COM 15
MYSTERY ROCK. Russia’s 2013 Chelyabinsk fireball source remains
elusive. Analysis of the top candidate shows unmatching composition.
Around 70,000 years ago, a
small star squeaked into our
solar system on a rapid flyby
that lasted for thousands of
years. Astronomers say the tiny
sun likely had minimal impact
on the Oort Cloud, a shell
of comets surrounding our
local neighborhood, but the
encounter serves as a reminder
that other perturbers might
lurk among nearby stars.
The dim object, informally
known as Scholz’s Star, was
noted in catalogs prior to the
discovery, but its location in a
crowded region of sky near the
galactic plane filled with other
small red stars made it anony-
mous. This one only eventually
stood out because it was so
close to Earth.
Simulations show the star
passed within about 0.8 light-
year of the Sun and is now
about 20 light-years away.
Scholz’s Star would have trav-
eled across our sky at a stun-
ning 70 arcseconds per year
— seven times faster than the
current champion, Barnard’s
Star. Despite that close pass,
the star would have been invis-
ible to the naked eye except
possibly during occasional
flare-ups.
Comets are blamed for some
30 percent of Earth’s craters
bigger than 6 miles (10 kilome-
ters) across. And in the past, sci-
entists proposed that a close
brush with another star could
hurl those ice balls our way. But
there’s scant evidence for
impacts hitting our planet in
waves. And searches so far have
found few stars that might have
passed inside the Oort Cloud,
even though scientists predict
these encounters could happen
12 times every million years.
And while Scholz’s Star is
interesting for passing closest,
experts say it’s extremely
unlikely that the flyby would
have more than a minimal
impact on the Oort Cloud,
meaning it would be unlikely
to have hurled comets at Earth.
Scientists suspect the
European Space Agency’s new
Gaia mission — built to survey
a billion stars and map the gal-
axy — will find stars that
passed even closer or will in
the future. — E. B.
Small star brushed Oort Cloud
Quasars are the brilliantly luminous objects
we see when intensely heated material
spirals in toward a supermassive black hole,
giving off enormous amounts of energy.
Their brightness means they are the most
distant, and hence oldest, objects we are
able to see in the universe. One newly dis-
covered quasar — with the catchy name
SDSS J0100+2802 — shines its light from
only 900 million years after the Big Bang,
with the luminosity of 420 trillion Suns. At
over 12 billion solar masses, it dwarfs the
supermassive black hole at the center of the
Milky Way by over 3,000 times. Scientists
from Peking University announced their dis-
covery in the journal Nature on February 26.
Astronomers know from black hole
observations both near and far that a gal-
axy’s growth is intricately connected to the
growth of its central black hole. But it is
unknown how this relationship might have
changed over the past 13 billion years. The
newly discovered black hole managed to
grow to an astonishing size at a time when
the first stars had only recently emerged, so
scientists hope this distant quasar can teach
them how galaxies formed and evolved in
the infant universe. — K. H.
Monster black hole found at cosmic dawn
CRUSHING THE COMPETITION. The most distant
known quasars are shown here, plotted by their mass
and brightness. The latest discovery easily outclasses
all of its fellows in both categories. ASTRONOMY: ROEN KELLY,
AFTER ESO/M. KORNMESSER
CLOSE CALL.
Scholz’s Star and
its companion
brown dwarf graze
our solar system in
this artist’s impres-
sion of the scene
70,000 years ago.
Our Sun shines in
the background.
MICHAEL OSADCIW/
UNIVERSITY OF ROCHESTER
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