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Poor astronomy | Star passing distorts a young star kindergarten

The sun flies solo through the galaxy, the nearest star to us over 40 trillion kilometers away. But that is not the case for all stars.

Many are in heaps, thousands of stars nearby, so close encounters are actually common. But if you rewind the clock, you will discover those stars formed in that cluster, so that there would inevitably be close to star passes, even when some of the stars are still enveloped in the huge disk of gas and dust from which they are formed. Another star passing by would gravitationally distort the disk, pull on it, and form patterns in the gas and dust.

A few objects similar to what is expected of such a passport have been seen, but the evidence was always unmanageable. However, new observations of a relatively nearby object change that game and show what is very similar to what is expected of a star interfering with a disk. It's not a lock, but it's very convincing.

About 3,700 light-years from Earth lies the Canis Major R1 association, a huge lump of gas and dust that actively forms stars in it. Two star clusters are formed, which contain many young stars.

Z Canis Majoris (or just Z CMa) is a member of one of these clusters. It is still formed, only a few hundred thousand years old, and is actually a binary, two stars in orbit around each other. One of the stars has about the same mass as the Sun, while the other is a fleshy 5 solar masses.

They are separated by more than 10 billion kilometers - more than twice as far as Neptune's distance from the Sun. They are embedded in a huge disk of gas and dust of over 200 billion km across, but each has a much smaller disk that surrounds them just a few billion km across. The smaller slices feed the material of the stars so that they grow. Sometimes planets are also formed on such disks.

But there is a mystery: A few years ago, infrared observations showed a muffled streamer coming out of the stars, a narrow dust finger several hundred billion kilometers long. Its origin was unknown, although a few ideas have been hovered, such as that it is the wall of a cavity carved out of an explosive outflow event from the young stars, or a spiral arm formed due to instability in the huge disk of dust , which surrounds the binary. However, everyone ran into problems, so no explanation was entirely satisfactory.

A team of astronomers can now have the solution (link to paper). New observations taken using the Atacama Large Millimeter / Submillimeter Array (or ALMA) in Chile and the Very Large Array in New Mexico show more detail close to the binary than ever seen before and also detect two new objects near the binary.

One that they call object C (A and B are the two stars in binary) appears to be another young star that may also have a slice of material around it. It is at least 700 billion km from binary. Object D is on the opposite side of the binary, closer to it, and is probably a lump of material fragmented away from the overall more even distribution of material around the stars.

What is so very interesting here is that the long streamer points away from the binary points right on Object C.

If object C is really a star and passes by the still formed binary, then its gravity will distort the disk and be able to pull a streamer of material out behind it as it pulls away. Such an encounter should also create a secondary arm of material that would also be pulled out in the opposite direction, and these deep images show it too - and it goes straight through Object D.

It is very interesting. Simulations that use physics for such an encounter mimic the observations quite well, adding weight to the idea that we are actually seeing an intruding star create chaos in the binary disk.

That in itself, however, is not a slam dunk. But there is more.

Young stars like these sometimes break out in bursts of energy that are thought to occur when more lumpy material from their disks falls on them. This generates a lot of energy that blows outward what we call one outbreak. Most young stars who do this spend somewhere between 1-10% of their time on eruptions.

But both stars in Z CMa are known to erupt, sometimes simultaneously. The chances of this happening are less than 1% random, provided their outbreaks are independent. But if Object C disturbs the disk, it is expected that the material further out will fall on the stars and create correlated eruptions from both stars. Since that's what's seen here, this also adds weight to the idea that we're watching a star interloper mix things up.

This story is connected, but that does not mean it is true. What is needed are deeper observations to reveal weaker material so that astronomers can try to unravel the structures around Z CMa and see if that streamer is physically connected to Object C, or if there is other evidence that the streamer was pulled away from the binary using C's gravity. It would also help to find more items like this; if we find more young stars with streamers pointing to other nearby stars, then we can be more confident that we are seeing a cosmic hit-and-run.

Of course, that's easier said than done, but lots of new observatories are being built all the time. Perhaps we will be able to hang a figure on how often such events occur and how it affects the construction of the young stars. We are constantly learning more about how stars and planetary systems are formed, and to be honest, there are still plenty of mysteries behind the birth and youth of our own solar system. All of these puzzle pieces will hopefully allow us to construct a meaningful picture of our own home, as it was ages ago.

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