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Starts With A Bang

3 Big Lessons We Can All Learn On The Hubble Space Telescope’s 30th Anniversary

Over the past 30 years, we’ve revolutionized what we know about the Universe. But we couldn’t have done it without these lessons.

On April 24, 1990, the Hubble Space Telescope rocketed into low-Earth orbit, where it’s remained for 30 years. It was serviced four times throughout its lifetime, correcting flaws, repairing and replacing on-board equipment and installing improved instruments. Even today, 30 years after its launch and 11 years after its final servicing, it remains the greatest space-based optical observatory in all of human history.

It’s easy to look back at the myriad of discoveries made with the Hubble Space Telescope and marvel at how they’ve revolutionized our view of the Universe, from the Solar System to the most distant reaches of deep space. But perhaps even more important than any specific discoveries are these three lessons, 30 years on, that illustrate how we’ve used this spectacular piece of equipment to advance our fundamental understanding of the cosmos.

From the distant Universe, light has traveled for some 10.77 billion years from distant galaxy MACSJ2129–1, lensed, distorted and magnified by the foreground clusters imaged here. The most distant galaxies appear redder because their light is redshifted by the expansion of the Universe, which helps explain what we measure as Hubble’s law. (NASA, ESA, AND S. TOFT (UNIVERSITY OF COPENHAGEN) ACKNOWLEDGMENT: NASA, ESA, M. POSTMAN (STSCI), AND THE CLASH TEAM)

1.) Whenever you can, look as you’ve never looked before. This was the fundamental motivation for even building and flying this observatory. Here on Earth, astronomers have no choice but to contend with our atmosphere. As transparent as it is to visible light, it’s still like viewing the Universe from the bottom of a swimming pool. Clouds, particulates, and even just the distortive effects of turbulent airflow all make it incredibly difficult to determine fine details about the Universe.

Even with the tremendous advances that adaptive optics have made over the past three decades, even with much larger telescopes available on the ground compared to Hubble’s modest 2.4-meter primary mirror, there are still enormous classes of observations that Hubble is uniquely suited for. In other words, it’s capable of viewing the Universe to greater precisions, depths, and in unique wavelength bands compared to any other observatory.

All of these images of the same target were taken with the same telescope (Hubble), but are at increasing wavelengths as you go from left to right. That is the reason why they have higher, sharper resolutions on the left. The leftmost images also have a higher frequency as well as a shorter wavelength; in the radio portion of the spectrum, we often talk about frequency instead of wavelength, for mostly historical reasons. (NASA, ESA, AND D. MAOZ (TEL-AVIV UNIVERSITY AND COLUMBIA UNIVERSITY))

This is, in many ways, the most important reason why Hubble is so valuable. It allows us to look at the Universe in a way that reveals things that no other observatory has ever revealed before. In particular, Hubble’s capabilities enabled:

  • the highest-resolution ultraviolet observations ever, including unprecedented ultraviolet spectroscopy (which the atmosphere forbids from the ground),
  • the ability to resolve objects as small as 0.05 arc-seconds, or 1/72,000th of a degree, without any adaptive system or software processing,
  • infrared wavelengths that go out to almost 2,000 nanometers, or three times the limit of the longest-wavelength light human eyes can see (and that cannot be well-observed from the ground due to atmospheric absorption),
  • and the ability to perform long-exposure astronomy due to the low noise levels from space, enabling deep-field views as never before.
Pluto, shown as imaged with Hubble in a composite mosaic, along with its five moons. Charon, its largest, must be imaged with Pluto in an entirely different filter due to their brightnesses. The four smaller moons orbit this binary system with a factor of 1,000 greater exposure time in order to bring them out. Nix and Hydra were discovered in 2005, with Kerberos discovered in 2011 and Styx in 2012. (NASA/M. SHOWALTER)

Sure, we’ve reached the limits of what Hubble can do on these frontiers, but these new limits are many times better than the pre-Hubble limits. Any time you push to fainter limits, greater wavelength coverages, wider observational fields-of-view, and higher resolutions, you’re able to see new objects and new details in those objects, eclipsing our previous knowledge sets.

Sometimes, the act of looking alone is enough to reveal new truths about the Universe. Hubble discovered:

among many others. Whenever you build a new tool, you unlock the capability of seeing the Universe as never before. With the James Webb Space Telescope, WFIRST, and a slew of new proposals on the horizon, humanity is poised to take the next great leap into the distant Universe.

30 protoplanetary disks, or proplyds, as imaged by Hubble in the Orion Nebula. Hubble is a brilliant resource for identifying these disk signatures in the optical, but has little power to probe the internal features of these disks, even from its location in space. Many of these young stars have only recently left the proto-star phase. Star-forming regions like this will frequently give rise to thousands upon thousands of new stars all at once. (NASA/ESA AND L. RICCI (ESO))

2.) Always follow the evidence, no matter where it leads. This is one of the most underappreciated lessons in all of science, and it particularly applies to the Hubble Space Telescope. We can see this by looking at the scientific motivation for even building and flying this telescope in the first place. It’s literally right there in its name: it’s named the Hubble Space Telescope not because it was to honor Edwin Hubble, but because its main science goal was to measure how quickly the Universe was expanding: to measure the Hubble constant.

The telescope was designed with the capabilities to perform those measurements, observing many different properties of galaxies to simultaneously determine their brightness, size, redshift, and a myriad of other properties. After 10 years of operations, they released the results of the Hubble Space Telescope Key Project, and did it: they successfully determined the rate at which the Universe was expanding.

Graphical results of the Hubble Space Telescope Key Project (Freedman et al. 2001). This was the graph that settled the matter of the expansion rate of the Universe: it was not 50 or 100, but ~72, with an error of about 10%. (FIGURE 10 FROM FREEDMAN AND MADORE, ANNU. REV. ASTRON. ASTROPHYS. 2010. 48: 673–710)

But along the way, Hubble taught us a whole slew of lessons that we weren’t anticipating. It helped determine that the Universe wasn’t just expanding, but that the expansion was accelerating: our Universe was dominated by dark energy. Even today, most of the data informing our best measurements of that accelerated expansion come from the Hubble Space Telescope.

We discovered how galaxies grew and evolved over cosmic time, determined when star formation peaks, measured precisely when in the distant past the Universe became fully ionized, showed us unprecedented details about how stars die, and even helped us learn what the age of the Universe is. It gave us spectacularly large numbers of galaxies that were — just by chance — serendipitously aligned with large intervening masses, producing images of gravitational lenses that are as spectacular as they are scientifically valuable.

A zoomed-in view of the gravitationally lensed supernova iPTF16geu. The insets shows a view of the foreground lensing galaxy and on the far right the resolve multiple images of the lensed supernova as observed with the Hubble Space Telescope and the Keck Telescope/NIRC2 instrument. (SDSS; ESA/HUBBLE & NASA; KECK OBSERVATORY; JOEL JOHANSSON)

In every single instance, we had theories and models that fit all the evidence we had at the time prior to Hubble concerning each of these scientific issues. After the Hubble data came in, the leading scenario concerning every single one of these phenomena needed to be revised in some way, from small tweaks to complete overhauls.

We were able to push the frontiers in ways that they had never been pushed before, and that led to new observations, new data, new results, and — in many cases — new and surprising conclusions. We built the Hubble Space Telescope with a particular science goal in mind, but its capabilities enabled us to explore corners of the Universe we didn’t even know existed at the time of the telescope’s design. We followed the evidence wherever it led us, and the Universe revealed secrets we didn’t even fathom it could possess.

This composite image of a region of the distant Universe (upper left) uses optical (upper right) and near-infrared (lower left) data from Hubble, along with far-infrared (lower right) data from Spitzer. The Spitzer Space Telescope is nearly as large as Hubble: more than a third of its diameter, but the wavelengths it probes are so much longer that its resolution is far worse. The number of wavelengths that fit across the diameter of the primary mirror is what determines the resolution. (NASA/JPL-CALTECH/ESA)

3.) There is a ‘right way’ to be wrong. Being wrong is one of the most important components of any scientific advance. You have a prevailing theory, that theory makes predictions, those predictions translates into observational or experimental tests, and you use the best investigative tools at your disposal to perform those tests. When you get your results, you never know what you’re going to find. Possibilities include:

  • they’re consistent with what the leading theory predicted, at least, within the errors,
  • they’re inconsistent with the prevailing theory’s predictions to some significant degree,
  • they’re consistent with a number of plausible alternatives, while excluding or disfavoring other alternatives,
  • or perhaps they point away from the consensus line-of-thought entirely, pointing to the need for a new direction or a new set of considerations.
When our Sun runs out of fuel, it will become a red giant, followed by a planetary nebula with a white dwarf at the center. The Cat’s Eye nebula is a visually spectacular example of this potential fate, with the intricate, layered, asymmetrical shape of this particular one suggesting a binary companion. At the center, a young white dwarf heats up as it contracts, reaching temperatures tens of thousands of Kelvin hotter than the red giant that spawned it. (NASA, ESA, HEIC, AND THE HUBBLE HERITAGE TEAM (STSCI/AURA); ACKNOWLEDGMENT: R. CORRADI (ISAAC NEWTON GROUP OF TELESCOPES, SPAIN) AND Z. TSVETANOV (NASA))

There are two paths to take that are very tempting, but are both scientifically dubious and even dangerous. One is to assume that the leading theory is correct, and to toss away outlier data until your results conform with what you expected. Another is to trust in your data entirely, irrespective of any other concerns, and to draw a speculative, even fantastic conclusion based on the novel results you’ve obtained.

But the responsible course of action is to analyse your new data as responsibly as you can, as though you didn’t know what the outcome implied, and then to draw your conclusions based on the full suite of data available: all of your new data plus all of the other data, including from complementary methods, that other researchers have collected. Only by synthesizing all of the relevant information together can we ever hope to form a fully consistent picture of our physical reality.

As we’re exploring more and more of the Universe, we’re able to look farther away in space, which equates to farther back in time. The James Webb Space Telescope will take us to depths, directly, that our present-day observing facilities cannot match, with Webb’s infrared eyes revealing the ultra-distant starlight that Hubble cannot hope to see. (NASA / JWST AND HST TEAMS)

Before Hubble, we did not know how fast the Universe was expanding. We did not know its age; we did not know how much matter was in it; we did not know whether its ultimate fate was to recollapse or expand forever. We did not know when stars and galaxies first formed, what the earliest ones were like, or the details of how stars were born and died. We did not even know whether there were planets in solar systems beyond our own.

Travel the Universe with astrophysicist Ethan Siegel. Subscribers will get the newsletter every Saturday. All aboard!

30 years later, we have the answers to all of these questions, largely thanks to scientific contributions made using this one astronomical observatory. New questions have arisen in their place, as pushing the cosmic frontier back to new depths always leads to the discovery of novel phenomena that themselves require an explanation. The cosmic frontier is truly endless in this regard. May we always remain curious enough to investigate and solve whatever mysteries the Universe lays before us.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.


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