The unexplained object is seen on the right hand side of this picture (Picture: Beltrami County Emergency Management)

Nasa researchers are investigating an unexplained incident in which a bright flash lit up the sky and caused a sound so loud it was compared to a sonic boom.

On Monday night, people living across a 50-mile radius in Minnesota reported witnessing a bright object streaking horizontally across the sky and heard a bang that rattled windows and shook their homes. 

Investigators believe the mystery object was the size of a refrigerator and ploughed into the atmosphere at a speed of between 30,000 and 130,000 miles per hour.   

Beltrami County Emergency Management revealed that the sonic boom was too close to the ground to be a meteor – or ‘at least not ones that don’t cause regional devastation.’

An email from Professor Juan Cabanela, a local physicist studying Monday’s mysterious event, suggested the timing of the boom indicated the object was no ordinary meteor.

‘I still don’t know what it was, but I was fairly confident it couldn’t be a meteor,’ he said in the email, seen by Mail Online. 

Three videos were of the incident were also obtained by Chris Muller, director of Beltrami County Emergency Management.

‘I don’t think it was a UFO in the sense of aliens and don’t want to sound that I do,’ said Mr Muller.

Despite multiple reports of the flash shining brightly in the sky on Monday night, he has not been able to confirm it was a flying object.

‘If it was anything that would have been airborne, it should have been picked up by radars,’ he said. ‘We did check with the [National] Weather Service, and they didn’t have anything on the radar. They also did not have any lightning detected.

‘So, we’re actually leaning towards that this was something that was on or near the ground.’

Is it a bird, is it a plane, or is it an insect? (Picture: Beltrami County Emergency Management)

The timing of the object’s flight path is a sign that the event was likely not a meteor on a consistent trajectory and acceleration.

Two videos show the journey of the object.

The first was a security video from a private home in Nymore, south of Lake Bemidji.

Mr Muller said it ‘clearly shows a very bright white/blue flash over the sky’ followed by a thunderous boom 2.95 seconds later.

The second video was captured at the Bemidji Regional Airport, four miles to the northwest of Nymore. It shows a super-fast white streak zooming past the airport.

‘This video was provided to an astronomer and a scientist from Nasa,’ said Mr Muller.

‘They analysed the video frame by frame and determined the object is too horizontal to indicate it was a meteor.

‘It is undetermined if the two videos are related.’

Beltrami County Emergency Management is exploring whether the sighting was caused by an exploding transformer in the power grid – but this has not been confirmed. 

Mr Muller has reviewed additional footage from the airport’s camera, from Monday night and at times during the day, and now suspects the sighting in that video can be explained.

‘There’s nothing that would have been interfering with the video camera, such as a wire or something like that reflecting light,’ he said.

‘But one obvious thing is that bugs were flying around.

‘And there were other bugs before that one. And it just so coincided that the timestamp on that was the exact same time as the other reports.’

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