1,000 AAS Nova Highlights and Five Years of Astronomy

In August of 2015, AAS Nova launched as a new service provided by the AAS journals. Today, five years later, we’re officially celebrating the milestone of the 1,000th Highlight post published on the site.

Beyond functioning as a news service, AAS Nova acts as an archive of astronomy research — which provides us with an interesting opportunity to explore how our understanding of the universe has developed.

Today we’re taking a moment to look back at a tiny sample of the new discoveries and ideas published across different corridors in the AAS journals and highlighted on AAS Nova over the past half-decade.

NGC 1052-DF2

The faint object in the center of this image is NGC 1052-DF2, an ultra-diffuse galaxy at the center of a scientific debate about dark matter. [NASA/ESA/P. van Dokkum (Yale University)]

Galaxies and Cosmology

As might be expected, the past five years have seen new records set for the galaxies we’ve spotted, from the densest galaxy to the faintest distant galaxy to some galaxies that — mysteriously — might be lacking dark matter entirely.

We’ve also continued to make progress toward resolving a number of long-standing debates, such as the question of why we don’t see as many small satellite galaxies as predicted (the “missing satellite problem”), or why our two methods of measuring the Hubble constant — a number that describes the rate of expansion of the universe — come up with different results.

black hole merger

Simulated image of two merging black holes, viewed face-on. LIGO announced the detection of ten of these events from its first two observing runs. [SXS Lensing]

High-Energy Phenomena and Fundamental Physics

One of the biggest headlines in the past five years was the first detection of gravitational waves from a merging pair of black holes. Since this discovery, the Laser Interferometer Gravitational-wave Observatory (LIGO) and its European counterpart, Virgo, have detected more than a dozen mergers of compact objects, and observatories across the world have searched for — and found! — electromagnetic counterparts to these collisions. Theoretical models of compact binary formation and evolution have also advanced in leaps and bounds as we’ve learned more.

Continuing the theme of “cool new observations of black holes”, the Event Horizon Telescope presented its view of M87 last year, opening a window onto what’s happening in the innermost regions around supermassive black holes. And we’ve amassed dozens of observations of black holes tearing apart passing stars in tidal disruption events, improving our models of this destruction in the process.

But outbursts from black holes aren’t the only transient phenomena flashing through our skies. The past few years have dramatically advanced our understanding of fast radio bursts, sudden, brief bursts of radio emission that originate from outside our galaxy. We now suspect these flashes might be related to high-energy phenomena, like the birth or evolution of distant magnetars.

HL Tau

This ALMA image of the protoplanetary disk surrounding the star HL Tauri reveals the detailed substructure of the disk, including gaps that may have been cleared by planets. [ALMA (ESO/NAOJ/NRAO)]

Interstellar Matter and the Local Universe

One of the biggest new players in the study of gas and dust in the local universe is the Atacama Large Millimeter/submillimeter Array (ALMA), which announced new results from its first long-baseline, high-resolution campaign around the time that AAS Nova first launched. Since then, ALMA has continued to produce spectacular observations — the array is mentioned in 82 of the 1,000 Highlights currently posted on AAS Nova, indicating the transformative nature of its observations.

As we peer deeper into interstellar clouds, we’ve also discovered a number of new molecules in the gas and dust of the universe, broadening our interstellar census and helping us to better understand our origins. Additionally, we’ve made significant advances in understanding the structure of magnetic fields in dense interstellar clouds and unraveling the role that they play in star formation.

Breakthrough Starshot

Artist’s illustration of the Breakthrough Starshot Initiative, a plan to send a fleet of tiny spacecraft to Alpha Centauri. [Breakthrough Initiatives]

Laboratory Astrophysics, Instrumentation, and Software

While the most headline-grabbing astronomy is often major detections and observations, more attention has started to come to the important underlying work of exploring astrophysical phenomena in the lab — from the construction of white dwarf photospheres to the formation of dust grains under conditions mimicking the cold vacuum of space — and developing new and increasingly advanced instrumentation and software.

New observatory designs like the CHIME radio array have come online and are already producing dramatic results, and scientists continue to produce clever algorithms for more advanced data analysis and new codes for simulating astrophysical sources and phenomena.

Human-made objects in space continue to both inspire and trigger debate. Recent developments include the Breakthrough Starshot Initiative to send a fleet of centimeter-sized spacecraft to the nearest star system, as well as the influx of satellites in low-Earth orbit and the impact this has on astronomy.

The Solar System, Exoplanets, and Astrobiology

The hypothetical Planet Nine made a splash nearly five years ago when it was first proposed as an explanation for the odd clustering of trans-Neptunian objects in our outer solar system. Significant theoretical and observational work has followed, but we still don’t know if there’s an unseen planet lurking in the outskirts of our solar system. 

Pluto and Charon

This composite image with enhanced colors shows New Horizons observations of Pluto (foreground) and Charon (background). [NASA/JHUAPL/SwRI]

On the small-body front, the New Horizons spacecraft flew by Pluto just before AAS Nova launched, and it then followed up with an up-close look at asteroid MU 69. Multiple interstellar asteroids have recently been observed as they pass through our solar system, and missions are underway to actually land on asteroids and return samples to Earth.

Recent exoplanet observations and models explore compact multiplanet systems, ultrashort-period hot Jupiters, and the atmospheres of extreme exoplanets. TESS launched in 2018 and has revolutionized exoplanet observations.

The number of detected Earth-like planets continues to grow, and we’re better exploring host stars’ habitable zones. New players have joined the search for extraterrestrial intelligence, and we’re learning more about promising targets for astrobiology searches as well potential biosignatures to look for. 

Parker Solar Probe

Artist’s illustration of the Parker Solar Probe. A special ApJS issue features around 50 articles detailing early results from this mission. [NASA/Johns Hopkins APL/Steve Gribben]

The Sun and the Heliosphere

In solar physics, we’ve continued to make steady progress toward solving major mysteries of our Sun, like how particles are accelerated in energetic solar flares, and why the outer solar corona is so much hotter than the layers of the Sun’s atmosphere that lie below it (the so-called coronal heating problem). We’re also gaining a better understanding of our broader solar system as the Voyager satellites and IBEX explore the heliosphere.

In addition to the large assortment of Sun-observing telescopes already on the job, we’re still finding new ways to explore our nearest star — from hard X-ray images to balloon-borne ultraviolet observations. An especially unique view is now coming from the Parker Solar Probe, a spacecraft that recently arrived at the Sun and is already producing results. This probe will continue to plunge ever closer to the Sun’s surface over the next five years.

red supergiants

Artist’s illustration of one of the most massive star clusters within the Milky Way. The center of the cluster contains 14 red supergiant stars. [NASA, ESA and A. Schaller (for STScI)]

Stars and Stellar

Simulations continue to advance and we’ve significantly improved our abilities to model and understand the dramatic deaths of massive stars. We’ve observed new oddities — like the baffling dimming of Boyajian’s star or the unusual transient known as the Cow — and we better understand the magnetic activity and flaring of cool M-dwarf stars, some of the best prospective hosts for habitable planets.

A huge astronomical milestone was achieved with Gaia’s first and second data releases, which map the positions, parallaxes, and proper motions for more than a billion stars and have enabled a wealth of studies of our surrounding galaxy.

There are, of course, many more astronomical successes from the past half-decade than could be summarized in a short post here. Even so, this look back on the past five years of astronomy provides a clear sense of the remarkable advances we’ve made in a relatively short time.

It should be noted that our advances don’t negate the challenges that our field still faces — we have plenty of problems to address, like racial diversity, equity, and inclusion in astronomy. Nonetheless, as we look both inward and outward, we’re making steady progress toward understanding the universe around us and our role in it.

At AAS Nova, we’ve loved reporting on all that’s happened in astronomy over the past five years. We’re excited to see what the next five bring!