Astronomy

ASTRONEWS

Mars Reconnaissance

Orbiter

80 , 000 megabits/sol

Mars

Odyssey

2 ,^20

0 m

egab

its/so

l

60

0 m

eg

ab

its/

sol

Curiosity

rover Opportunity rover

10

0 m

eg

ab

its

/so

l

FAST

FAC T

18 ASTRONOMY • DECEMBER 2015

3 FEET DEEP. Decades of data from NASA spacecraft show Earth is locked into at least 3 feet (1 meter) of sea level rise,

the agency said August 25. It’s less certain if that will happen within a century or take longer.

By peering deep into the cosmos to a time

when the universe was less than 4 billion years

old, scientists have uncovered key evidence

to help support a model of galaxy formation

that’s been hotly debated for over a decade.

Astronomers led by Christopher Martin of the

California Institute of Technology in Pasadena

have uncovered a swirling disk 400,000 light-

years across — what’s called a protogalaxy

— that is actively being fed by a filament con-

nected to the cosmic web of gas that extends

throughout the universe. “This is the first

smoking-gun evidence for how galaxies form,”

Martin says.

The discovery provides strong observational

support for the cold-flow model of galaxy

formation. This model posits that relatively

cold gas in the early cosmos from the interga-

lactic medium that makes up the cosmic web

is responsible for fueling rapid star formation

and therefore galaxy development.

Its competing standard model of galaxy for-

mation focuses on dark matter halo collapses

as the trigger, but this theory does not fit with

the fast star formation recently discovered in

galaxies that existed just 2 billion years after

the Big Bang. The cold-flow model can pro-

duce such rapid star birth and enough spin

to form extended rotating disks, but obser-

vational evidence had been lacking until this

protogalaxy discovery, which appeared in the

August 13 issue of Nature. Further, Martin and

his team already have found two additional

swirling disks that could provide more support

for the newer model. — K. F.

A distant clue to

galaxy formation

Physicists believe that the

majority of the universe is

composed of dark energy,

which they infer from obser-

vations but have so far been

unable to measure directly.

One reason for this could be

that dark energy particles

“hide” like a chameleon,

changing their mass depend-

ing on the density of mate-

rial around them. Thus in the

empty depths of space, the

particles would have strong

fields, able to push the cos-

mos apart, as modern theory

requires. But in a lab setting,

they would be weak and

almost impossible to detect.

In a study appearing in the

August 21 issue of Science,

physicists searched for these

elusive particles by creating

an extremely low-density

environment and watching

how individual atoms

behaved closer and farther

from a dense ball. They saw

no differences, but their work

was still able to rule out a

huge range of possibilities for

dark energy and limit the cha-

meleon fields to a million

times weaker than those of

gravity. — K. H.

Dark energy

hides like a

chameleon

5,

The solar masses contained in NGC 1313,

a newly identified intermediate mass

black hole. Astronomers say it’s just the

seventh of its kind now known.

MARTIAN ARMADA. NASA currently has five spacecraft studying Mars close-up. But when it comes to the

amount of information returned to Earth, the Mars Reconnaissance Orbiter (MRO) stands above all others. On

average, it returns about 80,000 megabits of data each martian day, or sol (one sol equals 1.03 Earth days).

This graphic compares MRO with the other three probes currently on extended missions. Because data rates

vary with Mars’ distance from Earth — in the same way a wireless connection slows down with distance — it

does not include the recently arrived MAVEN orbiter. ASTRONOMY: RICHARD TALCOTT, ROEN KELLY AND KELLIE JAEGER

BE AMING DATA

BACK HOME

The two orbiters relay most of Curiosity’s

and Opportunity’s data. MRO’s total includes

about 500 megabits/sol and Odyssey’s some

200 megabits/sol from the rovers.

MODEL PROTOGALAXY. Using the Cosmic Web

Imager, astronomers have discovered a distant pro-

togalaxy (circled) being fueled by a filament of cold

gas from the cosmic web (outlined). This is the first

observational proof for the cold-flow model of galaxy

SCIENCE IN A SPHERE.energy chameleon fields inside this Researchers looked for evidence of dark vacuum chamber, a hollow space formation. C. MARTIN/PCWI/CALTECH

with a trillionth the pressure of the air outside, which allowed them to

search for the sneaky signals. HOLGER MÜLLER