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Starts With A Bang

How has the Universe changed since last year?

In the grand scheme of the cosmic story, a single year isn't all that significant. But over time, the annual changes really add up!
map of universe
Looking out at any "slice" of the Universe allows us to see stars, galaxies, and the leftover glow from the Big Bang going all the way back a full 13.8 billion years to the start of the hot Big Bang. As the data clearly indicates, galaxies farther away have younger stars, are less massive and less evolved, and appear with greater number densities in space than they do today.
Credit: SDSS and the Planck Collaboration
Key Takeaways
  • All throughout the Universe, objects continuously interact with and influence one another. Over time, even the most stable physical systems don't remain perfectly constant.
  • That holds true for everything from the length of a day on Earth to the size of the observable Universe, all of which undergo small but substantial changes on a year-to-year basis.
  • As we celebrate the dawn of a new year, explore how some of the ways that our cosmos is different from how it was last year, knowing it'll never go back to the way it was again.

All throughout space, the Universe forever changes with each passing year.

This cutaway showcases the various regions of the surface and interior of the Sun, including the core, which is the only location where nuclear fusion occurs. As time goes on and hydrogen is consumed, the helium-containing region in the core expands and the maximum temperature increases, causing the Sun’s energy output to increase. When both hydrogen and helium are exhausted within the fusion-rich core region, the star will die.
Credit: Wikimedia Commons/KelvinSong

Our Sun, from internal nuclear reactions, loses ~1017 kilograms of mass per year.

The Earth orbits the Sun not in a perfect circle, but rather in an ellipse. The eccentricity, or the difference between the “long axis” and the “short axis” of our orbit, changes over time, while the Earth-Sun orbital period, which defines our year, changes slowly over the lifetime of our Solar System. If we neglect the other planets and the mass loss of the Sun due to the solar wind and nuclear fusion, we’d find that the total angular momentum of the Earth-Sun(-and-moon, if you like) system remains conserved.
Credit: NASA/JPL-Caltech

Earth consequently spirals outward, increasing our orbital radius by 1.5 cm (0.6 inches) annually.

Planet Earth, as viewed by NASA’s Messenger spacecraft as it departed from our location, clearly shows the spheroidal nature of our planet. This is an observation that cannot be made from a single vantage point on our surface, but there are many valid ways to measure the curvature of the Earth, all leading to the same conclusion.
Credit: NASA/MESSENGER

Gravitational interactions slow our planet’s rotation; days are 14 microseconds longer than last year.

When the Moon passes directly between the Earth and the Sun, a solar eclipse occurs. Whether the eclipse is total or annular depends on whether the Moon’s angular diameter appears larger or smaller than the Sun’s as viewed from Earth’s surface. Only when the Moon’s angular diameter appears larger than the Sun’s are total solar eclipses possible, a situation that will no longer be possible about 600-650 million years from now. Eclipses have been predictable phenomena for nearly 3000 years: since the time of the ancient Babylonians.
Credit: Kevin M. Gill/flickr

The Moon-Earth distance lengthens by 3.8 cm (1.5 inches) per year, rendering total solar eclipses rarer and shorter.

The changes in a one solar-mass star’s luminosity, radius, and temperature over its lifetime, from the start of nuclear fusion in its core 4.56 billion years ago until its transition into a full-fledged red giant several billion years from now, which is the beginning of the end for Sun-like stars. Although annual changes are small, their cumulative effects cannot be ignored for long.
(Credit: RJHall/Wikimedia Commons)

Stellar evolution causes our Sun to heat up, becoming 0.0000005% more luminous each year.

This one small region near the heart of NGC 2014 showcases a combination of evaporating gaseous globules and free-floating Bok globules, as the dust goes from hot, tenuous filaments at top to denser, cooler clouds where new stars form inside below. The mix of colors reflects a difference in temperatures and emission lines from various atomic signatures. This neutral matter reflects starlight, where this reflected light is known to be distinct from the cosmic microwave background.
(Credit: NASA, ESA and STScI)

Across the Milky Way, about 5 new, low-mass stars formed last year.

When a star-forming region becomes so large that it extends over an entire galaxy, that galaxy becomes a starburst galaxy. Here, Henize 2-10 is shown evolving toward that state, with young stars in many locations and active stellar nurseries in numerous locations galaxy-wide. If we were to count the number of stars within the galaxy and multiply that number by the Sun’s light-to-mass ratio, we’d underestimate the total flux by about a 3-to-1 ratio.
Credit: NASA, ESA, Zachary Schutte (XGI), Amy Reines (XGI); Processing: Alyssa Pagan (STScI)

That represents under 0.0000001% of the 45 billion solar masses of new stars formed annually throughout the observable Universe.

This illustration of superluminous supernova SN 1000+0216, the most distant supernova ever observed at a redshift of z=3.90, from when the Universe was just 1.6 billion years old, is the current record-holder for individual supernovae in terms of distance. In terms of brightness, it easily outshines an entire galaxy; in terms of power, it can rival most of the stars in the Universe, all combined together, for brief intervals.
Credit: Adrian Malec and Marie Martig (Swinburne University)

Approximately 50 million new supernovae occurred within the visible Universe last year.

universe temperature
At any epoch in our cosmic history, any observer will experience a uniform “bath” of omnidirectional radiation that originated back at the Big Bang. Today, from our perspective, it’s just 2.725 K above absolute zero, and hence is observed as the cosmic microwave background, peaking in microwave frequencies. At great cosmic distances, as we look back in time, that temperature was hotter dependent on the redshift of the observed, distant object. As each new year passes, the CMB cools down further by about 0.2 nanokelvin, and in several billion years, will become so redshifted that it will possess radio, rather than microwave, frequencies.
Credit: Earth: NASA/BlueEarth; Milky Way: ESO/S. Brunier; CMB: NASA/WMAP

The leftover glow of radiation from the Big Bang — the cosmic microwave background — is 200 picokelvin cooler than a year ago.

The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more, unobservable Universe just like ours beyond that. It’s unfair to associate any particular point with the center, as what we perceive is determined by the amount of time that’s passed since the light observed today was emitted, rather than the geometry of the Universe.
Credit: Frederic Michel and Andrew Z. Colvin/Wikimedia Commons; annotations by E. Siegel

Our cosmic horizon, limiting what we can see, grows yearly by 60 trillion km: 6.5 light-years.

This artist’s conception shows a logarithmic view of the observable Universe. The Solar System gives way to the Milky Way, which gives way to nearby galaxies which then give way to the large-scale structure and the hot, dense plasma of the Big Bang at the outskirts. Each line-of-sight that we can observe contains all of these epochs, but the quest for the most distant observed object will not be complete until we’ve mapped out the entire Universe. With each passing new year, another few tens of thousands of galaxies potentially become visible.
(Credit: Pablo Carlos Budassi)

The number of perceivable galaxies grows, too: by about ~35,000 annually.

unreachable
The size of our visible Universe (yellow), along with the amount we can reach (magenta) if we left, today, on a journey at the speed of light. The limit of the visible Universe is 46.1 billion light-years, as that’s the limit of how far away an object that emitted light that would just be reaching us today would be after expanding away from us for 13.8 billion years. Anything that occurs, right now, within a radius of 18 billion light-years of us will eventually reach and affect us; anything beyond that point will not. Each year, another ~20 million stars cross the threshold from being reachable to being unreachable.
(Credit: Andrew Z. Colvin and Frederic Michel, Wikimedia Commons; Annotations: E. Siegel)

But fewer stars can be reached; that number drops by ~20 million per year.

This image, perhaps surprisingly, showcases stars in the Andromeda Galaxy’s halo. The bright star with diffraction spikes is from within our Milky Way, while the individual points of light seen are mostly stars in our neighboring galaxy: Andromeda. Beyond that, however, a wide variety of faint smudges, galaxies in their own right, lie beyond. Individual stars can be resolved in galaxies up to tens of millions of light-years away, but that represents only one-in-a-billion galaxies overall. This image showcases both the power and limitations of Hubble.
Credit: NASA, ESA, and T.M. Brown (STScI)

Each year, the Universe’s changes accumulate, forever altering our cosmos.

This annotated, rotated image of the JADES survey, the JWST Advanced Deep Extragalactic Survey, shows off the new cosmic record-holder for most distant galaxy: JADES-GS-z13-0, whose light comes to us from a redshift of z=13.2 and a time when the Universe was only 320 million years old. This galaxy appears about twice as large, in terms of angular diameter, as it would appear if it were half the distance away: a counterintuitive consequence of our expanding Universe.
Credit: NASA, ESA, CSA, M. Zamani (ESA/Webb); Science credits: Brant Robertson (UC Santa Cruz), S. Tacchella (Cambridge), E. Curtis-Lake (UOH), S. Carniani (Scuola Normale Superiore), JADES Collaboration; Annotation: E. Siegel

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.


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