Astronomy

ASTRONEWS

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The first observed gravitational

waves from the merger of two neu-

tron stars was also the first event

observed in both gravitational waves

and electromagnetic radiation,

including gamma rays, X-rays, vis-

ible light, and radio waves. Based on

the corresponding electromagnetic

radiation received, astronomers are

now piecing together the merger’s

aftermath, finding that the resulting

remnant, likely a black hole, is sur-

rounded by a “cocoon” of material

trapping any jets it may be emitting.

This most recent model was pub-

lished December 20 in Nature, based

on observations of radio waves and

X-rays from the event. Radio waves

from the merger were first picked up

September 2, 2017, and grew stronger

over time. But in the simple model —

with a remnant both surrounded by a

shell of material from the explosion

and emitting narrow jets with

enough energy to punch through

that shell — radio emission should

grow weaker. Instead, if the shell

completely blocks and absorbs the

jets, they sweep up an enshrouding

cocoon of material that re-emits the

lost energy at other wavelengths. In

this case, both radio and X-ray emis-

sion should grow stronger.

When the Chandra X-ray

Observatory followed up in early

December, the remnant’s X-ray

emission had indeed brightened, just

as the cocoon model predicted. “The

gradual brightening of the radio signal

indicates we are seeing a wide-angle

outflow of material, traveling at speeds

comparable to the speed of light, from

the neutron star merger,” said Kunal

Mooley of the National Radio

Astronomy Observatory, the first

author on the paper, in a press release.

“It was very exciting to see our

prediction confirmed,” added co-

author Gregg Hallinan of Caltech. “An

important implication of the cocoon

model is that we should be able to

see many more of these collisions by

detecting their electromagnetic, not

just their gravitational, waves.” — A.K.

QUICK TAKES

STILL KICKING

Voyager 1 recently corrected a

slow drift off course by firing a

set of four small thrusters that

haven’t been used in 37 years.

• THE NEXT ISS
  Deep Space Gateway, a
  proposed Moon-orbiting
  space station, has already
  been flooded with scientific
  research requests.


• 
  

  EXCITONIUM EXISTS
  Scientists proved the existence
  of a form of matter called
  excitonium, which is created
  when a “hole” left by an
  escaped electron behaves like
  a positively charged particle.

  
  


• 
  

  UNDER PRESSURE
  New simulations suggest that
  meteoroids break up not only
  from surface pressure, but also
  from intense internal pressure
  caused by air infiltrating
  cracks and pores in the rock.

  
  


• 
  

  SOUTHERN SKY
  Australian astronomers created
  the most comprehensive map
  of the southern sky to date. It
  includes roughly 300 million
  stars and galaxies.

  
  


• 
  

  HELLO AGAIN
  An asteroid resembling a
  skull zoomed past Earth on
  Halloween 2015. It will return in
  November 2018, passing about
  a hundred times farther away.

  
  


• 
  

  WATER WOES
  Nearly 1,000 feet (300 meters)
  of Mars' surface water could
  have been absorbed into its
  crust and locked within
  mineral structures over time,
  according to an international
  team of researchers.

  
  


• 
  

  RETURN TRIPS
  NASA is evaluating two
  potential new missions.
  Dragonfly would explore the
  chemistry and habitability of
  Titan, and the Comet
  Astrobiology Exploration
  Sample Return (CAESAR)
  mission would bring back a
  sample of Comet 67P/
  Churyumov-Gerasimenko.

  
  


• 
  

  PULSAR PLANETS
  The habitable zone for a
  planet around a pulsar could
  be as large as Earth’s orbit
  around the Sun — if the
  planet is a super-Earth capable
  of sustaining an atmosphere
  up to a million times as thick
  as our own. — J.P.

  
  

Neutron star merger created a cocoon

HOME, SWEET HOME. Astronauts sampled 15 locations on the International Space Station as part of a microbial

survey. Analysis showed the microbial community aboard the ISS closely resembles those found in Earth-based homes.

How to weigh solitary stars

A star’s mass determines nearly everything about it,

from its life span and temperature to the way it will die.

Measuring mass is easiest in multiple-star systems, where

Newton’s laws of motion allow astronomers to infer mass

by mapping the stars’ orbits around each other. Solitary

stars, however, are much harder to weigh.

But a new method, designed for use with the

European Space Agency’s Gaia mission and NASA’s

upcoming Transiting Exoplanet Survey Satellite (TESS),

promises to revolutionize this type of measurement.

Developed by Vanderbilt University professor

Keivan Stassun and his colleagues, the method combines

the star’s total light and its parallax (a star’s apparent

motion in the sky relative to background stars as Earth

circles the Sun) to estimate its diameter. Then, based on

the way the starlight flickers over time, astronomers can

measure the star’s surface gravity. From its diameter and

surface gravity, they can derive the star’s mass. Stassun’s

group published their method December 15 in The

Astronomical Journal.

“We have shown that we can estimate the mass of

stars cataloged by NASA’s Kepler mission with an

accuracy of about 25 percent, and we estimate that it will

provide an accuracy of about 10 percent for the types of

stars that the TESS mission will be targeting,” said Stassun

in a press release.

Other methods of estimating the mass of lone stars

carry uncertainties of up to 100 percent. If a star has plan-

ets, astronomers can then misjudge their masses by up to

67 percent. A more accurate method for weighing single

stars promises the ability to gain vastly more insight into

these stars and their planets. — A.K.

NEW MODEL. The simple model (left) of a neutron star merger remnant spewing out narrow jets into a shell of debris was ruled out by

observations of increasing radio and X-ray radiation after August’s gravitational wave event. Instead, a new model (right) accounts for the

observations with a cocoon of material stopping and absorbing the energy from the jets, then re-emitting it over a wide angle. D. BERRY

WEIGHING IN. Accurately measuring the mass of solitary stars

will not only improve our understanding of these objects, but also

vastly improve estimates of the mass of any planets found circling

them. NASA/TIM PYLE