galaxy are sometimes call off “ cities of stars ” . If so , there is unfeignedly a “ Darkness on The Edge Of Town ” , not just because the asterisk become sparser at the edge but because dark matter takes over as the dominant material body of batch . Near the shopping center , however , stars and planets make up most of the galactic heart .
Ever sinceVera Rubindiscovered that the pep pill with which galaxies rotate require far more mass than could be reckon , astronomers have tried to pick up what make up this so - called “ dark matter ” . Resolving how this mystifying substance is distributed within galaxies is part of that quest . Professor Kenneth Freemanof the Australian National University has used a novel technique to provide an solvent .
From inside the Milky Way much of our own galaxy is blur , so astronomers study similar galaxy rather . “ We chose NGC 6946 , which is more than 22 million short long time away from Earth , ” Freeman said in astatement .
The way to work out drab affair ’s distribution , Freeman told IFLScience , is to get hold the overall distribution of pile and subtract thebaryonic(ordinary or non - dark ) topic . The first part has been done using the fastness at which stars orbit the astronomical center to calculate the total radial gravitational pull they are experiencing .
Measuring ordinary topic contribution has proven intemperately , but inMonthly Notices of the Royal Astronomical SocietyFreeman and colleagues use NGC 6946’splanetary nebulaeto find an solvent . Despite their name , planetary nebulae have nothing to do with planet . Instead , they represent a point in a star ’s last where stellar winds push its outer layers into immense diffuse formations . Although exceptionally brief by galactic standards , there are several hundred terrestrial nebula at any one time in a galaxy the size of NGC 6946 .
Planetary nebula let loose a distinctive green incandescence that if even slightly dispirited or red shifted reveals movement towards or out from us at even meek swiftness . When a astronomical disk face us , uranologist can quantify these nebulae ’s effort comparative to the astronomical plane , rather than the common stress on orbits in the woodworking plane . These drift say us the local gravitative forces from the disk . Since ordinary matter is jazz to be contract into the magnetic disk , compared to the skinny - globose distribution of dark matter , the new entropy earmark Freeman to determine the amount of ordinary mass at different distances from the astronomical center .
“ We ’ve discovered that stars and accelerator account for about three - quarters of the gravitational pull in the inner parts of the Milky Way and other spiral galaxies , ” Freemansaid . “ But the dark matter whole rule gravitational force in the out division of these galaxies .
Freeman acknowledged to IFLScience that the Milky Way ’s aggregated distribution may not equate NGC 6946 , despite their common spiral structure and similarity in mass . “ We ’re doing more extragalactic nebula in the same preference to us , ” he said . “ If they are all ordered we can generalise , and that seems to be what we are assure . ”
ask whether know the distribution has helped in understanding what gloomy matter is , however , Freeman answered : “ Nope . We have n’t a hint . ”
