Why a New Discovery Has Changed the Shape of the Milky Way | Unveiled

Why a New Discovery has Just Changed the Shape of the Milky Way

Our knowledge and understanding of space is always changing. More so than ever before, we’re filling in the blanks of the cosmos so that now the “great unknown” is just that little bit less unknown than it ever has been. But that can also mean that the things we thought we knew sometimes need to be changed and updated, to fall in line with modern findings and theories.

So, this is Unveiled, and today we’re exploring why a new discovery has changed the shape of the Milky Way.

For every second of your life on Earth you’ve also been a committed resident of the solar system and, thinking even further afield, of the Milky Way. This galaxy we call home is really quite a feat of cosmological balance and engineering. It’s at least 100,000 light years across, with some estimates reaching past 200,000 lightyears, and more. It holds upwards of 100 billion stars, with some models claiming upwards of 500 billion stars. There are billions more planets than even that to contend with, plus black holes, quasars, neutron stars, and an enigmatic supermassive black hole at the very centre, called Sagittarius A-star - according to most leading theories. And it’s all speeding through the universe - carrying us, our planet, and everything else - at comfortably more than a million miles per hour. When it comes to illustrating the sheer incredible-ness of this, our reality, few things do it better than taking just a couple of moments to contemplate the true nature of the Milky Way.

It’s no wonder, then, that scientists and astronomers have given countless hours of research to the Milky Way. To unpicking its mysteries and mastering its endless intricacies. Of all the problems and ponderings, however, the question of shape has gone largely unchallenged for many years. In general, we know that the Milky Way is what’s known as a barred spiral galaxy. In almost all depictions of it, there’s a central mass of stars - the bar - surrounded by swirling and elegant whooshes of yet more cosmic matter, to make up the spiral. The nearby Andromeda galaxy boasts a barred spiral shape, too, although there are various differences between these and all other galaxies in the form - particularly with regard to how tightly or loosely tied into the bar the arms of any one galaxy are. But, regardless, it’s the arms of the Milky Way that have been thrust under the spotlight in particular, via a new study.

According to a December 2021 NASA release - based on data taken from the Hubble Space Telescope - the Milky Way may be “more fluffy [and] less wiry”. The announcement relates to a Hubble study, conducted by a team at the Space Telescope Science Institute in Baltimore, in the state of Maryland. The study involved a specific technique to map the Milky Way by measuring the distances between dust clouds in a section of the Perseus Arm- which is one of the major spiral arms in the Milky Way.

With their sights set on the outer galaxy (that is, on a part of the galaxy that’s further from the galactic centre than the solar system is) the team converted their dust cloud measurements to conclude that the Perseus Arm - or this particular section of it, at least - is less ordered than previously thought. The material within it is far more spread out and seemingly random, meaning that the Perseus Arm itself is, as NASA describes, “more clumpy [and] less well organised”. In this way, the findings can be said to have changed the shape of the Milky Way because our understanding of the spiral whooshes has been significantly altered. More often than not, in artistic interpretations, the spiralling parts are shown to be clean and slender units. But the reality, it seems, is far messier than that. Which is oddly appropriate for another reason… because in the same announcement, one of the study leads, Josh Peek, explains how; “it’s a good possibility that the outer disk of the Milky Way resembles the nearby galaxy Messier 83, with shorter, chopped-up pieces of arms”. In the case of Messier 83, though, the pertinent name is more prominently a homage to one Charles Messier, the astronomer who first catalogued it in the 1780s.

Moving forwards, and the team behind this latest galactic study are already hoping to conduct a similar survey in the future, but next time on a part of the inner galaxy somewhere between the solar system and the galactic centre. And these plans have already been tied to the upcoming (and hopefully ground-breaking) facilities, the Nancy Grace Roman Space Telescope and the Vera C. Rubin Observatory. The Roman Telescope will be an infrared space telescope, and is currently tabled to launch in mid-2027. The Vera Rubin Observatory will be a ground-based telescope, currently scheduled to open in (or after) October 2023. Both should enable scientists and astronomers to peer into space with greater-than-ever clarity, which should make mapping the Milky Way a far easier task. Before long, then, we could find ourselves capable of picturing the Milky Way as though truly from the outside of it, looking in… and we could be generating far more detailed and accurate images of our home galaxy than even those we have today.

Still, some may question why science should be so interested in the first place? Why should we be so hung up on ironing out the details regarding the distribution of matter in a portion of a galactic arm that’s many, many lightyears away from us? What difference could that ever make? And, for the most part it’s perhaps true that anything we do glean from studying this deep into space isn’t about to change our daily lives today, next week or even next year. But the bigger picture remains vital, and the need to explore our surroundings far and wide continues to drive us forward.

As with so much about space, it’s also a case of getting a grip on the true scale of the universe. We now know that we can’t safely assume that even just the arms of just this galaxy should conform to a blanket, one-size-fits-all shape. We know that there’s room for so much more variation in the Milky Way, and - if we didn’t understand so, already - that the differences between this galaxy and the next and the next could effectively be endless. When we then consider that, at the top end of current estimates, there could be more than two trillion galaxies in the universe as a whole… it’s quite an eye-watering, mind-boggling, perspective-crushing thought.

Needless to say, though, we are making headway. And, in recent years, incredibly quickly. This latest study serves to better illustrate one particular aspect of our local region of space, but it’s also just the latest in an ongoing line of breakthroughs achieved. Up until around the early 1600s, the basic existence of the Milky Way itself had been debated for centuries, but not quite proved. From the seventeenth century onwards, the proof began to reveal itself. But, even then, it wasn’t until the early twentieth century - and the “Great Debate” in 1920 between the then-prominent scientists Heber Curtis and Harlow Shapley - that the idea of multiple, individual galaxies started to really take hold. And, once this fact of the universe was realised, the Milky Way - our galaxy - emerged as a standalone structure, in need of clear definition and shape.

It now seems as though we could be approaching the final stages of providing that. We might finally be imagining the Milky Way exactly as it is, and not just as a collection of predictions and suppositions. In this case, it can no longer be assumed that the Milky Way’s spiral arms conform to a clean and digestible shape. In reality, they’re far more awkward than that. They’re broken up, spread apart, and generally much more chaotic.

Again, as part of the study’s accompanying NASA announcement, Josh Peek summarises the impact that these findings may have. He says that though we’ve “long had a picture of the galaxy in our minds, based on a combination of measurements and inference… this work calls that picture into question”. In this particular field of astronomical study, it’s a turning point, with Peek reiterating that “we don’t see evidence that pieces we’ve been connecting up are actually connected”. And, in short, that’s why a new discovery has just changed the shape of the Milky Way.