Q&A: What is dark matter? And how do we know it exists?

 

Science Editor

What is dark matter?

It is everything we cannot see or detect in space. Scientists estimate that about 95 per cent of the Universe is composed of dark matter.

How do we know it exists if we cannot see it?

We know it is there from the gravitational effect it has on the objects we can see, like the stars and galaxies. Scientists estimate that about 24 per cent of the Universe is composed of this “missing mass”, with the rest made up of dark energy, which is forcing the Universe to expand at an ever-faster rate.

What is dark matter made of?

There have been two competing theories. One is that it is made of massive objects such as brown dwarf stars. The other that it is made of huge numbers of sub-atomic particles that do not interact with ordinary matter – it is these particles, known as neutralinos, that the Alpha Magnetic Spectrometer (AMS) is designed to detect.

How does the AMS work?

It cannot detect neutralinos directly, but can detect the particles given off when they collide in a process known as annihilation. The particles are in the form of electrons and their anti-matter partners, called positrons.

What are the results of AMS?

It has detected an excess of positrons, indicating the existence of neutralinos, but these could still come from distant pulsars – rotating neutron stars. More research is needed to resolve this.

Suggested Topics
Start your day with The Independent, sign up for daily news emails
ebooks
ebooksA special investigation by Andy McSmith
  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Ashdown Group: Field Service Engineer

£30000 - £32000 per annum + car allowance and on call: Ashdown Group: A succes...

Recruitment Genius: Sales & Marketing Co-Ordinator

£15000 - £17000 per annum: Recruitment Genius: Well established small company ...

Recruitment Genius: Internal Sales Executive - Hair & Beauty - OTE £25,000

£16000 - £18000 per annum: Recruitment Genius: This company supplies the ultim...

Recruitment Genius: Design, Marketing and Media Manager

£27000 - £29000 per annum: Recruitment Genius: This is an opportunity to join ...

Day In a Page

Not even the 'putrid throat' could stop the Ross Poldark swoon-fest'

Not even the 'putrid throat' could stop the Ross Poldark swoon-fest'

How a costume drama became a Sunday night staple
Miliband promises no stamp duty for first-time buyers as he pushes Tories on housing

Miliband promises no stamp duty for first-time buyers

Labour leader pushes Tories on housing
Aviation history is littered with grand failures - from the the Bristol Brabazon to Concorde - but what went wrong with the SuperJumbo?

Aviation history is littered with grand failures

But what went wrong with the SuperJumbo?
Fear of Putin, Islamists and immigration is giving rise to a new generation of Soviet-style 'iron curtains' right across Europe

Fortress Europe?

Fear of Putin, Islamists and immigration is giving rise to a new generation of 'iron curtains'
Never mind what you're wearing, it's what you're reclining on

Never mind what you're wearing

It's what you're reclining on that matters
General Election 2015: Chuka Umunna on the benefits of immigration, humility – and his leader Ed Miliband

Chuka Umunna: A virus of racism runs through Ukip

The shadow business secretary on the benefits of immigration, humility – and his leader Ed Miliband
Yemen crisis: This exotic war will soon become Europe's problem

Yemen's exotic war will soon affect Europe

Terrorism and boatloads of desperate migrants will be the outcome of the Saudi air campaign, says Patrick Cockburn
Marginal Streets project aims to document voters in the run-up to the General Election

Marginal Streets project documents voters

Independent photographers Joseph Fox and Orlando Gili are uploading two portraits of constituents to their website for each day of the campaign
Game of Thrones: Visit the real-life kingdom of Westeros to see where violent history ends and telly tourism begins

The real-life kingdom of Westeros

Is there something a little uncomfortable about Game of Thrones shooting in Northern Ireland?
How to survive a social-media mauling, by the tough women of Twitter

How to survive a Twitter mauling

Mary Beard, Caroline Criado-Perez, Louise Mensch, Bunny La Roche and Courtney Barrasford reveal how to trounce the trolls
Gallipoli centenary: At dawn, the young remember the young who perished in one of the First World War's bloodiest battles

At dawn, the young remember the young

A century ago, soldiers of the Empire – many no more than boys – spilt on to Gallipoli’s beaches. On this 100th Anzac Day, there are personal, poetic tributes to their sacrifice
Dissent is slowly building against the billions spent on presidential campaigns – even among politicians themselves

Follow the money as never before

Dissent is slowly building against the billions spent on presidential campaigns – even among politicians themselves, reports Rupert Cornwell
Samuel West interview: The actor and director on austerity, unionisation, and not mentioning his famous parents

Samuel West interview

The actor and director on austerity, unionisation, and not mentioning his famous parents
General Election 2015: Imagine if the leading political parties were fashion labels

Imagine if the leading political parties were fashion labels

Fashion editor, Alexander Fury, on what the leaders' appearances tell us about them
Phumzile Mlambo-Ngcuka: Home can be the unsafest place for women

Phumzile Mlambo-Ngcuka: Home can be the unsafest place for women

The architect of the HeForShe movement and head of UN Women on the world's failure to combat domestic violence