Although, when you look up at the sky, it may seem as though the stars are fairly well spread, star
formation actually isn’t regular throughout the universe. Mostly due to gravity, matter clumps up
and stars tend to form more in certain areas where lots of ingredients are available… while
other areas see no new stars being born, at all. And, as it turns out,
no new stars have formed around our own solar system in quite some time, apparently placing
us in the center of one of these barren regions. This is Unveiled, and today we’re answering the
extraordinary question; Did scientists just discover that we live in a cosmic bubble?
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It was a few decades ago when scientists first noticed something very strange about
our placement in the universe. In the 1970s, astronomers realized that new stars don’t form
anywhere near our solar system. And that all the closest stars to us are either very old and have
been there from the start… or are younger but have drifted closer over millions of years, meaning
they never formed especially nearby. This led researchers to theorize that there was a sort of
bubble they called the “Local Bubble” surrounding our system, determining that no new stars
have formed inside of this bubble for at least fourteen million years. Interestingly,
our solar system is almost directly in the middle of this seeming void, with barely any
new stars forming at all around us for around five hundred light years in all directions. Even
within the vast expanse of the universe we can class ourselves as decidedly cut adrift, then.
But new research may have finally shed light on how our local bubble operates.
The multi-authored study, published in January 2022 in the journal “Nature”, leads with the
headline “Star formation near the sun is driven by expansion of the local bubble”. Using data from
the European Space Agency’s Gaia Space Observatory and creating a 3-dimensional map through software
called Glue (created by one of the lead authors, Alyssa Goodman) researchers were able to create
a visualization of our bubble. Including its timescale, and its relationships to other,
nearby formations. So, what did they find? First, although it’s called the Local Bubble,
it’s not perfectly round by any means, and is shaped more like a blob. It’s around one thousand
light years long, and we’re positioned roughly in the middle… although that’s only by chance.
It’s suggested that our solar system just so happened to drift into the bubble around five
million years ago… and it’s expected to leave it in about another eight million years, or so. The
bubble’s insides or contents are otherwise mainly empty, but scientists still describe the space
as “a cavity of low-density, high-temperature plasma surrounded by a shell of cold, neutral gas
and dust”. As dramatic as that sounds, it means mostly empty space on the inside… lacking in
the ingredients necessary to birth stars. Chiefly, this analysis enables researchers
to understand why it is that we don’t have any new-born stars as neighbors. Broadly speaking,
stars form due to gravity pulling in large amounts of gas and dust until the mass gets so large that
the entire structure collapses in on itself and ignites. In order for that to happen, however,
you first need large amounts of gas and dust, but that’s not what we have on the inside of
the cosmic bubble. There’s some cosmic material, yes, but not nearly enough for star formation.
The leading theory as to why this is the case suggests that around fourteen million years ago,
a series of supernovas - perhaps fifteen in total - took place that reshaped the local spread of
star fuel. It’s thought that these supernovas created blast waves that pushed all the gas
and dust that had been here outwards, until it settled on what’s now the edge of the bubble...
at which point all of that accumulated star stuff began birthing new stars over and over again.
Which has evidently resulted in no stars for lightyears around… and then a flurry of star
activity at a certain distance away from us. According to the 2022 study, there are then
multiple regions relatively close by that do tend to birth new stars more so than
other areas… and they all sit somewhere near the surface of the bubble, but not inside of it. These
star clusters include Corona Australis, Perseus, Cepheus, and other major constellations.
Looking ahead to the future, while researchers believe that our bubble is still forming,
and it will continue to grow for the time being, it’s thought that it won't grow forever. The
bubble is currently expanding at a rate of about 4 miles per second, but that rate is not expected
to increase. In fact, it has been steadily decreasing since the last of the supernovas,
millions of years ago. Eventually the bubble will stop growing and start to lose its shape.
No one can be precisely sure when it will disappear entirely, but it’s thought likely
that by the time our own sun drifts out of this area (in eight million years from now)
there won’t then be a bubble left to exit. Rather, there may well be space and opportunity
for stars to more easily form again, in this region, as the universe continually evolves.
Importantly, it’s not as though our local bubble is held to be an anomaly in any way.
There are likely many more cosmic bubbles littered throughout the universe, formed and
operating in a similar manner. There are likely many more seeming voids, relatively lacking in
the conditions for star formation, but with an outer edge along which stars form freely. And,
actually, we’re already aware of a few that exist close to, and even intersect, our own.
One of these bubbles is called the Loop One Bubble. It exists around 330 light years from
the sun, and was also formed out of supernovas, pushed into being by the resulting stellar winds.
This bubble has tunnels that connect it to our own, as well… to the point where we might
imagine the two to be connected much as seas and oceans are on Earth. Other bubbles close to us
are the Loop 2 and Loop 3 bubbles. And, although researchers still aren’t sure on the details
of how this network of cosmic bubbles might affect one another, those behind the 2022 study
have compared the setup to plowing snow. What’s meant by this is that there are some regions,
along the edges of these bubbles, where the star dust (or snow) that’s pushed out
overlaps… and this is why we have some regions with far higher stellar birth rates than others.
We can see, then, that by analyzing these parts of space where seemingly not much happens,
we can begin to map and predict what’s unfolding all around us with greater accuracy. This research
is an important step forward toward understanding the complex layout of the Milky Way galaxy, and
also of the universe as a whole. It may be some fifty years since the idea of cosmic bubbles was
first floated within academic circles, but we’re now finally beginning to fashion visualizations of
the structures themselves. We’re now finally realizing the reality of our own bubble,
including how it formed and for how much longer we’ll be floating through it. But, more than that,
we also now know why it is that we seem to be in a region that’s so barren of new star formation.
Importantly, there are still millions of stars, in general, to be found within our bubble. It’s just
that they’re likely either older than fourteen million years (when the first supernovas unfolded)
or they didn’t form here and have just drifted this way. After all, that’s what happened with our
own sun. It passed through on its own magnificent voyage millions of years ago, and it won’t pass
out the other side for millions of years more. It's another incredible process to show just how
staggering the universe really is. In beauty, mystery, and intrigue. Even when, seemingly,
nothing’s happening, no stars are forming, and we’re surrounded by literally hundreds of
light-years of barren space… there are still some amazing things taking place. Cosmic explosions
from millions of years ago are still shaping our surroundings, and the stars that twinkle in the
sky are still only just revealing their true stories. It’s a long voyage of exploration and
knowledge… and that’s how scientists discovered that we live in a cosmic bubble.
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