Modern Australian

We discovered a warped and twisted disc of young, massive stars at the edge of our Milky Way

  • Written by Richard de Grijs, Associate Dean (Global Engagement) and Professor of Astrophysics, Macquarie University

From a great distance, our Milky Way would look like a thin disc of stars that rotates once every few hundred million years around its central region. Hundreds of billions of stars provide the gravitational glue to hold it all together.

But the pull of gravity is much weaker in the galaxy’s far outer disc. Out there, the hydrogen clouds that make up most of the Milky Way’s gas disc are no longer confined to a thin plane. Instead, they give the disc an S-like, warped appearance.

Although the Milky Way’s warped hydrogen gas layer had been known for decades, in research published today in Nature Astronomy, we discovered that a disc of young, massive stars there is warped too, and in a progressively twisted spiral pattern.

Read more: From pancakes to soccer balls, new study shows how galaxies change shape as they age

We were able to determine this twisted appearance after having developed the first accurate three-dimensional picture of the Milky Way’s stellar disc out to its far outer regions.

Mapping the Milky Way

Trying to determine the real shape of our galaxy is like standing in a Sydney garden and attempting to determine the shape of Australia. The Milky Way is all around us, so to determine its shape, we would need to map the distributions of stars in all directions.

While that is not particularly difficult in directions above and below the stellar disc plane, it becomes much harder along the Milky Way’s plane.

Other than stars and hydrogen gas clouds in the Milky Way’s plane, our view is obscured by huge quantities of dust. The material astronomers call dust is made up of carbon particles. It is not too different from the soot that builds up in your home if, for example, you have an open fire.

Large quantities of dust obscure our view of what lies beyond, but dust also makes light look redder. This is because the size of those carbon particles is close to the wavelength of blue light. Therefore, blue light can be absorbed quite easily by the dust while red light passes through without too much trouble.

But it’s not just the presence of dust that makes mapping our Milky Way galaxy troublesome. It is notoriously difficult to determine distances from the Sun to parts of the Milky Way’s outer disc without having a clear idea of what that disc actually looks like.

Pulsating stars

One of the researchers in my international team – Xiaodian Chen of the National Astronomical Observatories (Chinese Academy of Sciences) in Beijing – compiled a new catalogue of well-behaved variable stars known as classical Cepheids. These stars vary in brightness over a period of time.

These stars are among the best mileposts in astronomy: they can be used to determine very accurate distances with uncertainties of only 3-5%. This is pretty much as good as it gets in astronomy, allowing us to obtain the most accurate map of the outer Milky Way available to date.

Our new catalogue was based on observations made with NASA’s Wide-field Infrared Survey Explorer (WISE), a space telescope fitted with long-wavelength (infrared) glasses, ideal to look through any dust in the Milky Way’s disc.

The Cepheids mapped range from the Milky Way’s centre to its outer regions with most on the near side of the centre of our galaxy because of observational limitations.

Classical Cepheids are young stars that are some 4 to 20 times as massive as our Sun, and up to 100,000 times as bright. Such high stellar masses imply that these stars live fast and die young, burning through the hydrogen fuel in their stellar interiors very quickly, sometimes in only a few million years.

Cepheids show day- to month-long pulsations, which can be observed quite easily as changes in their brightness. Combined with a Cepheid’s observed average brightness, the period of its pulsation cycle can be used to obtain an accurate distance.

We all warp together

Somewhat to our surprise, we found that our collection of 1,339 Cepheid stars and the Milky Way’s gas disc follow each other closely. Until our recent study, it had not been possible to tie the distribution of young stars in the Milky Way’s outer disc so well to the flaring and warped disc made up of hydrogen gas clouds.

We discovered a warped and twisted disc of young, massive stars at the edge of our Milky Way 3D distribution of the classical Cepheid variable stars in the Milky Way’s warped disc (red and blue points) centred on the location of the Sun (shown as a large orange symbol). The units kpc are kiloparsecs (1 kpc = about 3,262 light years) along the image’s three axes are used by astronomers to indicate distances on galaxy-wide scales. Richard de Grijs (Macquarie University), Author provided

But perhaps more importantly, we discovered that the stellar disc is warped in a progressively twisted spiral pattern.

Many spiral galaxies are warped to varying extents, such as the galaxy ESO 510-G13 (pictured top) in the southern constellation Hydra, roughly 150 million light-years from Earth. However, only a dozen other galaxies were known to also show similarly twisted patterns in their outer discs.

Read more: Curious Kids: Where are all the other galaxies hidden?

Combining our results with these earlier observations, we concluded that the Milky Way’s warped and twisted spiral pattern is likely caused by forced torques from the galaxy’s massive inner disc. The rotating inner disc is, in essence, dragging the outer disc along, but since the outer disc’s rotation is lagging the resulting structure is a spiral pattern.

This new map provides a crucial update for studies of our galaxy’s stellar motions and the origins of the Milky Way’s disc. This is particularly interesting given the wealth of information we anticipate to receive from the European Space Agency’s Gaia satellite mission.

Gaia aims to eventually map our Milky Way in unprecedented detail, based on the most accurate distance determinations to the galaxy’s brightest stars ever obtained.

Authors: Richard de Grijs, Associate Dean (Global Engagement) and Professor of Astrophysics, Macquarie University

Read more http://theconversation.com/we-discovered-a-warped-and-twisted-disc-of-young-massive-stars-at-the-edge-of-our-milky-way-110985

NEWS

Lies, obfuscation and fake news make for a dispiriting – and dangerous – election campaign

The integrity of Australia's election process is under unprecedented pressure during this election.Wes Mountain/The Conversation, CC BY-NDThe integrity of Australia’s electoral processes is under unprecedented challenge in this federal election.The...

What's the school cleaner's name? How kids, not just cleaners, are paying the price of outsourcing

In Victoria in 1992, every government-employed school cleaner was terminated overnight.from shutterstock.comThis is an edited extract from The New Disruptors, the 64th edition of Griffith Review. It is a little...

how Western attitudes towards Islam have changed

Muslim clerics and members of the Pakistani Christian minority light candles to commemorate the victims of this week's bomb blasts in Sri Lanka. Islamic State has claimed responsibility for...

Vital signs. Zero inflation means the Reserve Bank should cut rates as soon as it can, on Tuesday week

The last time inflation was zero the Reserve Bank cut rates twice. It'll get the chance on May 7.ShutterstockWhat do US pizza executive Herman Cain, US conservative commentator Stephen Moore...

Bizarrely distributed and verging on extinction, this 'mystic' tree went unidentified for 17 years

Flowers of the mystical Hildegardia australiensis. I.D. Cowie, NT Herbarium.Author provided (No reuse)Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at...

Why the idea of alien life now seems inevitable and possibly imminent

Relative sizes of planets that are in a zone potentially compatible with life: Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f and Earth (named left to right; except for Earth, these are artists' renditions).NASA...

Think you're allergic to penicillin? There's a good chance you're wrong

A rash people assume is a reaction to penicillin may not be related to the drug at all.From shutterstock.comAre you allergic to penicillin? Perhaps you have a friend or relative...

'you’re always commenting on power'

Podcasters can introduce new voices to the conversations about the cities we live in.Salim October/ShutterstockMore and more podcasts about cities are being produced by journalists and academics. They’re being recorded...

you have the chance to stop fuelling devastation in the Amazon

Deforestation in the Amazon has accelerated since Brazilian president Bolsonaro scrapped environmental laws.ShutterstockThe effects of European consumption are being felt in Brazil, driving disastrous deforestation and violence. But the destruction...

All is forgiven in the Liberal embrace of Palmer

This election is acquiring quite a few back-to-the-future touches.There’s John Howard, in robust campaign mode. One of those he’s spruiking for is the embattled Tony Abbott, with a letter to...

Bat and bird poo can tell you a lot about ancient landscapes in Southeast Asia

A bat in a cave among the poo.Christopher Wurster, Author providedThe islands of Sumatra, Borneo and Java were once part of a much larger landmass connected to Asia called Sundaland...

Islamic State has claimed responsibility for the Sri Lanka terror attack. Here's what that means

In the wake of any tragedy, it should be enough to grieve and stand in solidarity with those who mourn. With a massive toll – at least 359 dead and...

Popular articles from Modern Australian

What to Do When Traveling From Australia to USAWhat we should know about ‘nitric oxide’ and why we need more of itDownsizing: What Is Too Small?5 unique ways to extract toxins from your bodyThe Art Of Bell-RingingModern Snapback Hats trending in Australia6 Mistakes to Avoid When Moving Overseas5 Tips Designed to Help Accentuate Your Hourglass FigureRoyal Edinburgh Military TattooThe inaugural Bondi Ocean Lovers FestivalHow to Plan a Remodeling at Home: Tips and TricksAchieving Facial Symmetry with RhinoplastyHow to Choose the Best Colors for Your BedroomFind Here the 3 Best Online Pokies in AustraliaHair Loss and Transplant Solutions