Conspiracy theorists say power source could be behind U.S. spy plane

Now an expert says the noises sound like a 'pulse detonation engine'

An expert claims the loud bangs which baffled Britons last night sounded like a type of experimental jet engine - which conspiracy theorists enjoy linking to a rumoured spy plane.

Dr Bhupendra Khandelwal added his comparison to a debate which began when hundreds of Twitter users from Aberdeen to Devon - and even New York - reported 'explosions' which shook windows and disturbed sleeping children at around 10pm.

One resident in Croydon, South London, recorded the sounds on her phone in a mystery that has left Britons blaming meteors, an 'alien invasion', 'the end of the world'... or just fireworks.

Could it be? An artist's image of the so-called Aurora project. Enthusiasts say one possible power source is a 'pulse detonation engine', whose sound is said to resemble that caught on an audio clip last night (below)

Dr Khandelwal, an engineering research associate from Sheffield, is among a team of scientists working on the technology behind types of 'pulse detonation engine'.

'It makes the same kind of pulsing sound as the one on this audio,' he told MailOnline.

‘When we run a test engine it’s a real industrial noise and you can hear it for miles. We have people coming to us asking to make less noise or keep it to the daytime.'

The engine works by using the force from a series of explosions, caused by mixing a fuel mist and air intake, to thrust itself forward. It can theoretically power planes at five times the speed of sound.

The technology builds upon 'pulsejet' principles which first emerged in the early 1900s and were used in German V-1 flying bombs.

Test flights using the most recent forms of the technology have lasted only a few seconds, but it is still listed by conspiracy theorists as a possible way of powering the so-called Aurora spy jet.

The theorists have cited 'Aurora' – a name which appeared in a Pentagon budget report in the 1980s – as an ongoing spy plane project for several years.

Officials routinely deny it exists. Of course, that has not dampened the spirits of the theorists, who point to a sighting of a mysterious triangular object by a North Sea oil engineer in August 1989.

Last year Lockheed Martin also unveiled plans for a spy plane that could fly at Mach 6, twice as fast as its famed SR-71 Blackbird, and said a missile demonstrating the new technology could fly as early as 2018.

Dr Khandelwal was keen to distance himself from the world of conspiracy theories, though he conceded there could always some things unknown to the public.

‘Of course we can’t know for sure if someone else could have the technology already,' he said.

Loud noises: People from Croydon (left) to Glasgow (right) were left baffled by a string of bangs last night

One possible explanation is that the loud noise and ground shaking could have been a meteorite breaking up in the atmosphere, which would result in a sonic boom - but this was dismissed by another expert

‘We can’t say for sure what this sound was,' he added. 'It's possible, but even if it was a PDE, I think half an hour would be a bit too long!'

Steven Aftergood, a government secrecy expert at the Federation of American Scientists, said: 'If an aircraft is responsible, then it’s worth noting that it may not be local at all.

'Because the sound wave that causes the boom can be reflected by the stratosphere, the source of the event could conceivably be hundreds or thousands of miles away from the place where it is heard on the ground.'

But Dr Andrew Taylor, a senior lecturer in aviation at Buckinghamshire New University, said the noises did not sound like a normal sonic boom.

If an aircraft is responsible, then it’s worth noting that it may not be local at all... The source of the event could conceivably be hundreds or thousands of miles away Steven Aftergood, Federation of American Scientists

'With smaller fighter jets just a single boom would be heard, or, as with Concorde, a "double boom" might be heard from larger aircraft as both the nose and tail cause shock waves,' he said.

'It sounds like gunfire or other ammunition, similar to what I used to hear as a child growing up in Lincolnshire when the RAF & USAF aircraft used to do bombing runs on the east coast bombing ranges.

'It could be geological or meteorological, but certainly not aeronautical in my opinion.'

Many Twitter users suspected sonic booms, similar to ones which shook Kent last month when two RAF jets intercepted a Latvian cargo plane in British airspace.

But a Ministry of Defence spokesman told MailOnline last night she had no records of any jets being scrambled.

Some suggested unusual weather conditions might be the source, but the Met Office dismissed those claims and said there was nothing out of the ordinary.

A spokesman told MailOnline: 'It definitely wasn't meteorological'.

The Metropolitan Police said there had been a fireworks display in Croydon, but Twitter users insisted that could not explain sounds in Bedfordshire, Glasgow, North Devon, Leicestershire and West Sussex.

At around the same time, a loud boom was reported by a number of people in the upstate New York areas of Buffalo, Cheektowaga and Clarence more than 3,000 miles away.

People described it as loud enough to shake their homes and rattle windows.

Theories: There was no shortage of ideas when it came to the possible source of the noises

Claudia Angiletta, who recorded the sounds in Croydon, south London, said she was watching TV at home when the unexplained sounds started.

She told MailOnline: 'I was just at home watching TV when I couldn't hear the program due to the loud noises. It was very distracting as it went on for ages.

'I went out to look for fireworks but I couldn't see anything in the sky. That's when I recorded the clip to send to my family to see if they could hear the same thing.'

The 27-year-old said that her family, who live roughly seven miles away in Norbury, south London, could also hear the sounds, which lasted for about 30 minutes. She then turned to Twitter to see if anyone could explain what they were.

Within minutes Twitter users had started spreading hashtags from the straightforward (#loudbangs) to the slightly melodramatic (#omgwereallgoingtodie).

Reaction: There was an explosion of activity on Twitter, where some users came up with their own theories

Many of the reports were picked up by Twitter user Virtual Astronomer, who said space debris re-entering the earth's atmosphere could have been responsible.

'Space debris such as old satellites and things can cause sonic booms heard over very large areas,' he told MailOnline. 'It's the same for big meteors or rocks that come in.

'There was very little wind last night so conditions were perfect for sound to travel very long distances.'

Science writer David Dickinson was among the experts who dismissed the meteor theory.

He told MailOnline that there was one piece of debris from Russian satellite Kosmos 2251 scheduled for re-entry, but said that the timing was 'not a good fit' for it to have been over the UK.

He added: 'I do not think it was a meteor or a piece of space-junk, as the noises mentioned spanned a large segment of time. Plus, unless it was cloudy over the U.K., there would've been visual sightings.

#Spooked: Was it an alien invasion, a meteor, the Third World War - or simply a few stray fireworks?

Dave Reed, who lives in Fareham, Hampshire, said his dogs 'went crazy for a couple of minutes' after hearing what he had assumed were fireworks.

The noises prompted conspiracy theories and immediate claims of a 'media blackout'.

Twitter user Carrie Proctor wrote: 'This is how we'll find our that WW3 has begun. It'll be a Twitter hashtag long before any official announcement!'

One MailOnline reader heard similar noises in Belgium.

Hyacinth Fahsi, who lives in Grimbergen, near Brussels, said the sound at 11pm local time - the same time as it was heard in Britain - woke his daughter and matched the recording in Croydon.

Describing the sound as 'repetitive explosions', he said: 'I first thought it was firework but it was different. Maybe thunder, but the sky was clear and I didn't see lightning, even far away.

'I wasn't thinking about it until my wife read your article.'