All About Space - UK (2020-02)

MYSTE RIE S

UNIVER SE

OF

THE

THE G

OBJECTS

BY THE NUMBERS

G objects that have been

found so far

Size of the G objects

inkilometres

Longestorbitalperiodofa

Gobjectinyears

YearthefirstGobjectwas

firstobserved

Numberoflightyears

betweenEarthandSgrA*

That’s 100 timesthe

distancebetweentheEarth

andtheSun

Number of light years from

the black hole Sgr A*

Shortestorbitalperiod

ofa Gobjectinyears

YearSagittariusA*was

firstdiscovered

Theimmensemassof

theblackhole

6

15

billion

1,600

2005

26,000

0 .1 3

170

1 9 74

4 million

sunS

Atthisstage,G2couldhavebeentreatedasan

outlier– a strangeobjectbehavingoddlyalone.But

someyearsearlierin2005,astronomershadalso

discoveredanotherstrangeobjectclosetoSgrA*.

InlightofG2,thisbecameknownasG1,anditset

GhezwonderingwhetherG1andG2couldbepart

ofa largerclassofobjects.

Assuch,togetherwithhercolleagues,Ghez

subsequentlywentbackover 13 yearsofdata

takenfromobservationsfromtheW.M.Keck

ObservatoryinHawaii,andfoundevidencelinking

fourmore.ThesebecameknownasG3,G4,G5and

G6,collectivelyknownastheGobjects.Certainly,

theywerelookeduponbyastronomerswithgreat

excitement.“Suchobjectshadnotbeenseenbefore

inanyotherenvironment,”saysMarkMorris,a

UCLAprofessorofphysicsandastronomywho

workedwithGhezonthestudy.

“Bystellarstandardstheirdustphotospheresare

verycold,andbecausetheyareina regionwitha

strong background of ultraviolet radiation they are

partially ionised and show up in emissions from

very hot hydrogen atoms, which again hasn’t been

seen elsewhere. They also appear to be present only

inthe entourage of the black hole.”

G3 through to G6 follow a different orbit to G1

and G2 around the supermassive black hole, which

points to them having developed independently of

each other, even though their behaviour in relation

toSgr A* was determined to be the same. “In

every passage the tidal forces of the black hole can

remove some of the material from the outer layers

ofsome of the G objects,” Morris says. “We actually

observed that happening for both G1 and G2.”

“Thetidalforcesof theblack

holecan removesomeofthe

materialfrom theouterlayers

of someoftheg objects” MarkMorris

Above: The

objects may

originate

from binary

stars forced to

merge under

the intense

influence

of Sgr A*

Right: When

observing G2

on its approach

to the cloud

using the ESO’s

Very Large

Telescope,

astronomers

were able

to work out

where on

its orbit the

different parts

of the cloud

were located

© ESO

© ESO