Australian Sky & Telescope - 02.2019 - 03.2019

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team,ledbyAlexanderScholz(University

ofSt.Andrews,UK),attheforefrontof

these searches. SONYC’s studies of the

star-forming regions NGC 1333 in Perseus

andRCW38inVela,aswellasoftheRho

Ophiuchus cloud complex, have turned up

abrowndwarf-to-starratioofbetween0.2

and0.5.Inotherwords,foreverybrown

dwarfinthisregion,therearetwotofive

stars.Thenumberofbrowndwarfscouldbe

higher if some of the stars host brown dwarf

companionsthathaveyettobedetected.

Extrapolating from this, Scholz’s group

calculates that there could be as many as

100billionbrowndwarfsinhabitingthe

Milky Way Galaxy. Yet these numbers fail to

add up in the Sun’s neighbourhood, where

theratioofbrowndwarfstostarsisjust

0.13,orabout1to8.

Themysterybehindthisdearthofnearby

brown dwarfs deeply puzzles Sergio Dieterich

(Carnegie Institution for Science), who is

alsoamemberoftheRECONSconsortium.

“Tryingtounderstandwhythishappensis

somethingIlosesleepon,”hesays.

In an effort to reconcile the observations,

Dieterichismodellingthecoolingrates

ofbrowndwarfstofigureoutifthere

could be more brown dwarfs in the Sun’s

neighbourhood that remain undetected

becausetheyaretoocoldtoemitatthe

observedwavelengths.Browndwarfsspend

theirentirelivescoolingaftertheyform,and

thosethatRECONSandSONYCseehave

temperaturesinthe1500Kto3000Krange,

which means they must be fairly young.

However, NASA’s Wide-field Infrared

Survey Explorer (WISE) was optimised to

findcoolobjects.Thecoldestbrowndwarf

yetdiscoveredisWISE0855−0714,whichhas

asurfacetemperatureofsome250K(−23°C).

YetWISE’s2012surveymaysupportthe

RECONS findings, by detecting on average

justonebrowndwarfforeverysixstarsin

the solar neighbourhood.

Iftherearemany,mucholderbrown

dwarfs that have cooled to become too faint

forevenWISEtosee,maybeScholziscorrect

andtherearemorebrowndwarfsoutthere.

SNGC 1333This composite image combines X-ray (pink), infrared

(red), and optical data (red, green, blue) of the cluster NGC 1333,

populated with stars that are less than 2 million years old. The X-ray

data reveal 95 young stars, 41 of which had not been identified in

infrared because there was no glow from a surrounding disk.

WSEEING DOUBLE (OR TRIPLE, OR.. .)Of

the 317 star systems in the solar neighbourhood,

85 have more than one component (ie. a star or a

browndwarf).That’samultiplicityfractionof27%.

= 1 system

SIRIUS At apparent

magnitude −1.46, Alpha

Canis Majoris is the

brightest star in the sky

and lies 8.6 light-years

from Earth.

2 components

3 components

4 components

5 components

1 component