Science

NASA has found a break in a spiral arm of the Milky Way that stretches 3,000 light-years

NASA has found a ‘break’ in one of the spiral arms in the Milky Way galaxy that could give new detail about the galaxy’s past.

The discovery, which looks ‘like a splinter poking out from a plank of wood,’ according to NASA, stretches 3,000 light-years across from one of the galaxy’s arms and includes stars and a group of four nebulae.

It is the first major structure identified that is situated so differently than the corresponding arms and is a significant find, given that researchers still do not know the full structure of the galaxy itself, as Earth is inside it.

NASA has discovered a ‘break’ in one of the spiral arms in the Milky Way galaxy

The discovery looks 'like a splinter poking out from a plank of wood,' NASA said. The structure stretches 3,000 light-years across and includes stars and four nebulae

The discovery looks ‘like a splinter poking out from a plank of wood,’ NASA said. The structure stretches 3,000 light-years across and includes stars and four nebulae

‘It’s akin to standing in the middle of Times Square and trying to draw a map of the island of Manhattan,’ NASA wrote in a statement.

The experts were able to find the feature using NASA’s Spitzer Space Telescope – before it retired in January 2020 – along with data from the European Space Agency’s Gaia mission to measure the precise distance of the stars in the arm. 

According to the ESA, the Gaia spacecraft, launched in 2013, is designed to create a three-dimensional map of the Milky Way with ‘unprecedented positional and radial velocity measurements.’  

After looking at the data, the scientists were able to determine that the ‘broken’ structure is moving at almost the same speed and direction in space as the arm itself, known as the Sagittarius Arm.

‘A key property of spiral arms is how tightly they wind around a galaxy,’ said the study’s lead author, Caltech astrophysicist Michael Kuhn, in the statement

The experts were able to find the feature using NASA's Spitzer Space Telescope (pictured) - before it retired in January 2020

The experts were able to find the feature using NASA’s Spitzer Space Telescope (pictured) – before it retired in January 2020

‘Most models of the Milky Way suggest that the Sagittarius Arm forms a spiral that has a pitch angle of about 12 degrees, but the structure we examined really stands out at an angle of nearly 60 degrees.’

This is done by measuring the arm’s pitch angle and comparing it to a circle, which has a pitch angle of 0 degrees. 

However, new observations suggest the structure ‘really stands out at an angle of nearly 60 degrees,’ Kuhn added. 

‘When we put the Gaia and Spitzer data together and finally see this detailed, three-dimensional map, we can see that there’s quite a bit of complexity in this region that just hasn’t been apparent before.’ 

The newly discovered structure also contains four nebulae – the Eagle Nebula (which contains the Pillars of Creation), the Omega Nebula, the Trifid Nebula, and the Lagoon Nebula.     

A nebulae is an interstellar cloud of gas, dust and hydrogen in space.

It is the first major structure identified situated so differently than the corresponding arms

It is the first major structure identified situated so differently than the corresponding arms

It's still unclear why the structure and the arm have vastly different angles

It’s still unclear why the structure and the arm have vastly different angles

It’s still unclear why the structure and the arm have vastly different angles. 

Scientists are not yet sure how or why arms on galaxies – in this case, spiral arms – form, but the discovery could shed light on that. 

‘Ultimately, this is a reminder that there are many uncertainties about the large-scale structure of the Milky Way, and we need to look at the details if we want to understand that bigger picture,’ said one of the study’s co-authors, Robert Benjamin, in the statement. 

‘This structure is a small piece of the Milky Way, but it could tell us something significant about the Galaxy as a whole.’ 

The study was published in July in the scientific journal Astronomy & Astrophysics

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