Imagine studying science in a lab that is thousands to trillions of miles away from you. You can’t touch anything, and you can’t control the experiments – all you can do is watch the events unfold.
This science is called astronomy.
The timescales on which the Universe builds, grows, and destroys its structures are stupefying – thousands of years to cough up a planetary nebula, tens of millions of years to make a star, billions of years to make a habitable planet…as humans, we simply cannot expect to ever see, first hand, these events unfold in their entirety.
Thankfully, the Universe is large enough that we can piece together a timelapse of the events in stages, as instances of it are happening to different systems across the Cosmos.
All astronomers use information carried on beams of light to learn how the Universe’s cosmic experiments are coming along. (The term light is just an abbreviation for a huge range of electromagnetic radiation given off by nearly everything in the Universe.)
The most plentiful form of light that our cosmic experiments give off is radio wavelength light. It is also the weakest of the energies given off by the Universe’s diverse experiments.
A typical radio wave carries a billionth the energy of an optical one. Even cell phone signals swamp cosmic signals. However, that has not stopped us from inventing state-of-the-art technologies for receiving these fascinating cosmic broadcasts.
With them we see the invisible Universe, the experiments of beginnings, endings, order, and mayhem.
Structure of the Universe
We live on a planet that orbits a star, the Sun. Our Sun is one of billions of stars that orbit around a disk-shaped structure called a galaxy. Our Milky Way Galaxy is one of several dozen in the Local Group of galaxies. The Local Group is a rural member of the Virgo Supercluster, a collection of 100 similar galaxy groups. Millions of superclusters give structure to the infinite Universe.
Mapped across space, the superclusters sketch out a kind of spherical webbing, like a snapshot of jumbled soap bubbles, with major galaxy clusters hanging out where the bubbles merge, and minor clusters, like the Local Group, residing farther into the voids.
How did the Universe get this bubbly shape?
The Big Bang
The Big Bang was the primeval event that brought all space and time, all matter and energy, into being. For several hundred thousand years immediately thereafter, the Universe was a very hot soup of particles and radiation. Light was trapped inside this mayhem.
As the Universe cooled, the first hydrogen and helium atoms began to form, assembling from those free-floating particles. When the particles became occupied in atoms, light finally had a chance of finding a path around them and out into space, giving us our first look at the young Universe.
Images taken by the Wilkinson Microwave Anisotropy Probe (WMAP) surveyed the entire microwave-length radio sky to map this very distant escape of light. WMAP showed us that indeed, the Universe was starting to take shape even in those early times. But were the clumps the seeds that grew into the first galaxies?
Some astronomers believe the universe was built with small pieces, such as gas clouds and star clusters, that merged over time to form galaxies and clusters of galaxies. Others theorize that the early Universe broke first into colossal clumps that contained enough building materials to make structures on the grandest scale — great walls and sheets of millions of galaxies — that fragmented into increasingly smaller gas and clouds, ultimately resulting in individual galaxies.
Astronomers would like to understand how density fluctuations in a sea of subatomic particles could have formed the great variety of galaxy shapes and sizes that make up the Universe as we see it today. And understanding galaxy evolution is necessary for addressing the even more fundamental questions about the expansion of space and the ultimate fate of the Universe.
Astronomers using ALMA are observing galaxies in their early phases, as they were 10 billion years ago, and will establish the star-forming history in near and distant galaxies.