This Is Why Every Galaxy Doesn’t Have The Same Amount Of Dark Matter
“It isn’t the properties of one or two galaxies that will be the ultimate test of dark matter, however. Whether these galaxies are generic dwarf galaxies or our first examples of dark matter-free galaxies isn’t the point; the point is that there are hundreds of billions of these dwarf galaxies out there that are presently below the limits of what’s observable, detectable, or having their properties measured. When we get there, especially in the distant Universe and in post-interaction environments, we can fully expect to truly find this yet-unconfirmed population of galaxies.
If dark matter is real, it must be separable from normal matter, and that works both ways. We’ve already found the dark matter-rich galaxies out there, as well as isolated intergalactic plasma. But dark matter-free galaxies? They might be right around the corner, and this is why everybody is so excited!”
When the Universe was first born, everything was uniform. There was dark matter and normal matter everywhere, in the same 5-to-1 ratio in all structures. But then the Universe had to go and get messy. It formed stars and galaxies of different masses and sizes, and that’s where the trouble started. In large, massive galaxies, even cataclysms like supernovae or active supermassive black holes don’t eject very much normal matter. But in small galaxies, significant amounts of normal matter can get ejected, upping that ratio to dozens or event hundreds to one. That ejected matter doesn’t just go away, but can itself, at least in theory, form dark matter-free galaxies. Where are we in our understanding of galaxies, dark matter, and gravitation?
It’s just a small piece of the puzzle, but this explains why not every galaxy has the same 5-to-1 ratio you might naively expect!
Scientists Discover The Loneliest, Most Isolated Galaxy In The Entire Universe
“The spirals and ellipticals in our backyard showed us, a century ago, that the Milky Way wasn’t alone. Even earlier astronomers still had copious bright galaxies they could observe with their telescopes. By measuring the speeds and distances of these galaxies, we discovered the expanding Universe. Without them, we might never have understood our cosmic origins: the hot Big Bang. Unfortunately, not every observer in the Universe gets so lucky.”
When we look out at the Universe, we see stars, galaxies, and galaxy clusters grouped together and aligned in a great cosmic web. Together, they make up the large-scale structure of the Universe. Observing these distant galaxies is what led us to our current scientific knowledge of all that’s out there, including about the Big Bang, dark matter, and many other fascinating properties.
But between these vast clumps of structure are enormous cosmic voids, containing very low numbers of galaxies. One such void is some 200 million light-years in diameter, and contains only one known galaxy in it: MCG+01-02-15, which is known as the loneliest galaxy in the Universe. If we lived there instead of in our Milky Way, we would not have discovered even a single galaxy beyond our own until we had reached 1960s-era levels of astronomical capabilities.
Come learn about the loneliest galaxy in the Universe, and see why we’re fortunate to be located here instead of there!
Galaxy Clusters Are Where Galaxies Like The Milky Way Go To Die
“When a galaxy enters a rich, massive cluster, it has to contend with two murderous factors. A single major merger can use up all the gas in both progenitor galaxies, leading to a red-and-dead elliptical galaxy. Even without one, the intracluster medium is rich in matter, and speeding through it can strip out a galaxy’s gas. Without that gaseous presence, new stars can no longer form.”
Here in our Local Group, our Milky Way forms stars at a low but steady rate, and will likely continue to do so for billions of years. It’s only our impending major merger with Andromeda that will use up all of our gas, and turn us into a giant elliptical without the capacity to form new stars. If we were more isolated, we could continue to form stars for trillions of years: many times the age of the Universe.
But if we were in a rich galaxy clusters, our demise would be not only certain, but much more rapid. Here’s the proof.
What Was It Like When The Milky Way Took Shape?
“The cosmic story that led to the Milky Way is one of constant evolution. We likely formed from hundreds or even thousands of smaller, early-stage galaxies that merged together. The spiral arms likely formed and were destroyed many times by interactions, only to re-form from the rotating, gas-rich nature of an evolving galaxy. Star formation occurred inside in waves, often triggered by minor mergers or gravitational interactions. And these waves of star-formation brought along increases in supernova rates and heavy metal enrichment. (Which sounds like everyone’s favorite after-school activity.)
These continuous changes are still occurring, and will come to a conclusion billions of years in the future, when all the galaxies of the Local Group have merged together. Every single galaxy has its own unique cosmic story, and the Milky Way is just one typical example. As grown up as we are, we’re still evolving.”
We normally think of events in the past of having occurred at a specific time. Star formation began in the Universe when it was 50-to-100 million years old. The first galaxies formed some ~200 million years after that. The Universe became transparent to visible light 550 million years after the Big Bang, and star formation reached its maximum between 2 and 3 billion years after the Big Bang.
But when did the Milky Way form?
That’s a silly question, as it turns out, because what we know as the Milky Way has been constantly evolving and growing over time. Had we come along billions of years ago, or were we to come along billions of years in the future, our galaxy would be unrecognizable to us.
Here’s the story of how the Milky Way took shape, and what it was like along every step of the way. You might be surprised!
This Is How We Will Discover The Most Distant Galaxy Ever
“Sometime in the distant past, likely when the Universe was less than 2% its current age, the very first galaxy of all formed when massive star clusters merged together, resulting in an unprecedented burst of star formation. The high-energy light from these stars struggles to escape, but the longer-wavelength light can penetrate farther through neutral atoms. The expansion of the Universe redshifts all the light, stretching it far beyond anything Hubble could potentially observe, but next-generation infrared telescopes should be able to catch it. And if we observe the right part of the sky, with the right instruments, for a sufficiently long time to reveal the right details about these objects, we’ll push back the cosmic frontier of the first galaxies even farther.
Somewhere, the most distant, first galaxy of all is out there, waiting to be discovered. As the 2020s approach, we can feel confident that we’ll not only shatter the current cosmic record-holder, but we know exactly how we’ll do it.”
13.8 billion years ago, our Universe as-we-know-it began with the hot Big Bang. There were no stars or galaxies back then; there weren’t even bound structures of any type. Everything was too energetic, and would immediately be destroyed by the unfathomably high temperatures and energies that every particle possessed. Yet, with time, the Universe expanded and cooled. Protons, nuclei, and neutral atoms formed; overdense regions gravitationally pulled-in mass and matter; stars were born, lived, died, and new stars were born in their aftermath. At some point, the first large star clusters merged together, passing a critical threshold and forming the first galaxy in the Universe.
That’s what we want to find. We’ve gone back to when the Universe was just 3% its present age, but that’s not enough. We must go father. We must find the first one. Here’s how we’ll do it.
The Brightest Galaxy In The Universe Is Surprisingly Young And Tiny
“In 2015, a new record was set for the brightest known galaxy, thanks to observations with the WISE telescope. Supermassive black holes power Extremely Luminous Infrared Galaxies. The brightest ones shine 10,000+ times as bright as our Milky Way.Although the Universe is just 10% of its current age and the galaxy is even smaller than ours, it outshines them all.”
I want you to close your eyes and imagine the Milky Way: a typical galaxy. Now, imagine a different galaxy, the brightest one you can think up. What does it look like? How do you imagine it?
Do you imagine something large, massive, with hundreds or even thousands of times as many stars? Do you imagine something that’s built itself up over billions of years? Well if that’s what you imagined, prepare to be shocked! The brightest ones of all are young, ultra-distant, and even smaller than our own galaxy!
Here’s the brightest galaxy in the Universe, which is turbulent, dusty, and looks nothing like you might expect!
Ask Ethan: How Many Galaxies Have Already Disappeared From Our Perspective?
“So how many earth observable galaxies have dropped out of sight? That is, how many galaxies (with the highest redshift) have disappeared from our point of view?”
When we look out at the distant reaches of space, there are some 2 trillion galaxies observable within our Universe. But our Universe is expanding, the expansion is accelerating, and light can only travel at the speed of light. Does that mean that galaxies are dropping out of sight?
There are two ways to look at this: from the point of view of not being able to see galaxies that we can presently see, and from the point of view of whether we can see the light those galaxies are emitting today, 13.8 billion years after the Big Bang? If we take the first definition, not only is the answer “zero,” but there will be trillions more galaxies revealed to us over time. But if we take the second, we find that most of the galaxies we can see today are already gone.
How many galaxies have already disappeared from our perspective? The cosmic implications should motivate us to get out there and explore while there’s still some good Universe left to go and see!
When Will We Break The Record For Most Distant Galaxy Ever Discovered?
“Finally, beyond a certain distance, the Universe hasn’t formed enough stars to reionize space and make it 100% transparent.
We only perceive galaxies in a few serendipitous directions, where copious star-formation occurred.
In 2016, we fortuitously discovered GN-z11 at a redshift of 11.1: from 13.4 billion years ago.
But recent, indirect evidence suggests stars formed at even greater redshifts and earlier times.“
It was only a couple of years ago that we set the current record for where the most distant galaxy is: from 13.4 billion years ago, when the Universe was just 3% its current age. This record is unlikely to be broken with our current set of observatories, as discovering a galaxy this distant required a whole bunch of unlikely, serendipitous phenomena to line up at once. But in 2020, the James Webb Space Telescope will launch: an observatory optimized for finding exactly the kinds of galaxy that push past the limits of what Hubble can do. We fully expect to not only break the record for most distant galaxy ever discovered, but to learn, for the first time, exactly where and when the first galaxies in the Universe truly formed.
Until then, it’s lots of fun to speculate as to when and where they might be, but it will take the observations of a lifetime to smash this cosmic record!
Astronomers’ Hopes For Pristine Stars Dashed: They’re Polluted After All
“In 2011, we found the first evidence for unpolluted, pristine gas, but it hadn’t yet collapsed to form stars.
But even bigger news came in 2015, when the galaxy COSMOS Redshift 7 (CR7) was discovered.
From 13 billion years ago, helium lines were observed, without any carbon or oxygen lines.
The hope was that CR7 contained stars made of hydrogen and helium alone.”
In 2015, the galaxy COSMOS Redshift 7 (CR7) was discovered. Its distance is so great that its light is arriving after a 13 billion year journey, meaning it comes from when the Universe was only 6% its current age. Earlier observations, taken with Hubble, showed the presence of hydrogen and helium, but not of heavier elements like carbon, nitrogen or oxygen. Could this be the first example of Population III stars: the first stars made from the pristine material left over from the Big Bang? For years, astronomers thought it just might be, but new observations in the radio from ALMA have crushed those dreams. Looking for the long-wavelength signature of singly-ionized carbon, they’ve found it everywhere, surrounding all the individual, independent components of galaxy CR7.
It may be extremely metal-poor, but it isn’t truly pristine. Come get the full story in images, video, and no more than 200 words. Talk less, smile more.