At leftover , a extensive view of the Dragonfly 44 galaxy , and at right wing , a stopping point - up of the same figure of speech , let on its large , elongate chassis and nimbus of ball-shaped clusters of stars around its core , similar to the gloriole that ring the Milky Way . mental image credit : Pieter van Dokkum , Roberto Abraham , Gemini Observatory / nimbus
An unusual galaxy , made up almost entirely of exotic “ dark matter , " has left astronomer and physicists scratching their heads . The galaxy , known as Dragonfly 44 , is locate some 300 million light - years from our own Milky Way and is about the same size of it as our galaxy — but a simple 100th of 1 percent of it is made up of ordinary matter . The rest—99.99 percent — is dark thing .
Dragonfly 44 in reality has about as much dark topic as our galaxy , but it has far fewer stars . As a result , the dark matter almost wholly dominates . “ It ’s kind of a dark twin of the Milky Way , ” wind researcher Pieter van Dokkum of Yale University tellsmental_floss .
The findings were published today inAstrophysical Journal Letters[PDF ] .
First aim in the thirties , dark matteris a mysterious form of matter trust to report for more than one - one-quarter of the stack and vigor in the cosmos . ( A great dimension — more than two - third gear — is the even - more - mysteriousdark energy ; a mere 5 percent of the macrocosm is made of average , seeable matter . ) Dark subject does n’t interact with ordinary matter — it ca n’t be come across with ocular or radio telescope — but its mien can be deduced through the gravitational tugboat that it exerts .
The fact that dour issue overtop over unconstipated affair is not by itself a surprisal : In most galaxies , van Dokkum excuse , there ’s about 50 times as much dark matter as ordinary affair . But in Dragonfly 44 , that ratio is even more extreme , thanks to the want of stars .
The only other galaxies be intimate to be this heavy skewed toward dark affair are the small gnome extragalactic nebula that revolve the Milky Way . But Dragonfly 44 is n’t like those galaxies — rather , it ’s just as heavy and monolithic as the Milky Way itself . How it ended up so dingy matter – expectant , and with so few maven , is a secret . “ We thought we sympathize these [ more monolithic ] wandflower quite well , ” says van Dokkum . “ They usually have a comparatively belittled amount of morose issue , in proportion to the number of stars that they have . This coltsfoot turns that on its fountainhead . ”
Because of the paucity of stars , Dragonfly 44 is extremely faint . It ’s one fellow member of a new class ofdiffuse , dim galaxiesdiscovered lately using theDragonfly telescope array , an innovative imagery system that uses ultra-“fast ” commercial telephoto lense ( the kind that play photographers use ) to find dense physical object in the night sky . The inspiration of van Dokkum and University of Toronto astronomer Roberto Abraham , Dragonfly was tailor - made to discover objects with “ low surface brightness level ” : While the igniter from stars is concentrated in specific point in the sky , galaxies are dim and their Inner Light is spread out — and these peculiar galaxies are even dimmer , and thus even harder to see . “ These object had always been missed , but with the Dragonfy scope , we found them , ” van Dokkum say .
Later , he and his co-worker aimed Hawaii ’s Keck telescope at Dragonfly 44 for a closer facial expression ( because the galaxy is so dim , this need pile up data over six night ) . They were able to measure the amphetamine of some of the galax ’s asterisk , from which the full mass of the extragalactic nebula can be calculated . From the brightness and the mass , they specify how much mass is “ missing”—that is , they infer how much extra mass must be present in the cast of dark affair , so as to keep the galaxy from vanish aside . Observations with the Gemini North telescope , also in Hawaii , revealed a aura of spherical clusters of stars hem in the galaxy ’s essence — similar to the halo known to surround our own milklike Way . “ Ultimately , we may learn about the link between dark issue and these mysterious star clusters , ” van Dokkum says .
Meanwhile , the bragging mystery of all remains the identity of the dark matter itself . Physicists ’ in effect guess is that it ’s made up of some kind of primordial particle , perhaps created at the metre of the big bang — but numerous attempts to detect such speck directly ( including the most recent effort ) have issue forth up empty . And Dragonfly 44 , being so far aside , is n’t likely to help much — but in principle , other dark matter – dominated galaxy could still be wait detection , much close to dwelling house . “ If we found a galax like this , that ’s close to us — that might be the idealistic place to look , to make a lineal sensing of the dark matter particle , ” van Dokkum says .
David Spergel , a Princeton University astrophysicist who was not necessitate in the current enquiry , tellsmental_flossthat these low surface – brightness galaxies “ are useful ‘ laboratories ’ both for studying the property of dark thing and understanding Galax urceolata formation . ”
