Play Live Radio
Next Up:
0:00
0:00
0:00 0:00
Available On Air Stations
Support NHPR's local journalism that brings clarity, context, and community!

Mapping The Seen And Unseen

This image shows the galaxy MCS J0416.1–2403, one of six clusters targeted by the Hubble Frontier Fields program. The varying intensity of blue haze in this image is a mass map created by using new Hubble observations combined with the magnifying power of a process known as gravitational lensing.
M. Jauzac, J-P. Kneib and the CATS collaboration
/
ESA/Hubble/NASA
This image shows the galaxy MCS J0416.1–2403, one of six clusters targeted by the Hubble Frontier Fields program. The varying intensity of blue haze in this image is a mass map created by using new Hubble observations combined with the magnifying power of a process known as gravitational lensing.

The invisible and unseen has always fascinated us humans.

Mapping both literal and metaphorical has always been about our quest for knowing.

As an astrophysicist, my research work involves mapping dark matter, the elusive substance that accounts for about a quarter of our universe. This is, though, not the first attempt to map the unknown. The deep fascination with the mysterious, and the impulse to seek and locate ourselves in the cosmic context, seems to be imprinted in our DNA and psyches.

Curiosity propelled the ancients to travel beyond familiar shores and to build instruments to chart both the terra firma's extent — and their place on it. The night sky offered a different perspective — and our ancestors sought connections between the predictable rise and fall of the heavenly orbs and earthly events — rain, storms and floods, as well as the reigns of emperors and the outcomes of wars. They exploited the regularity of the cosmos to navigate both their locations and their lives.

History shows us that it was the powerful confluence of ideas and instruments that spurred an age of exploration in the 13th through 15th centuries, leading humans to discover new continents and peoples. Slowly they defined the contours of the known continents, discovered new ones and documented, in their maps, an improving understanding of their world.

Maps were continually being made and re-made. For instance, the shift away from Ptolemy's world map, depicting the known world in 1492, to the maps produced in the 16th through 18th centuries reveal the leaps and bounds by which humanity's cartographic knowledge grew.

A page from a 1492 copy of Ptolemy's world map from his <em>Geographia</em>.
/ Library of Congress
/
Library of Congress
A page from a 1492 copy of Ptolemy's world map from his Geographia.

And the corresponding charts of the cosmos improved in turn. Demiurges, appearing in one early depiction of the cosmos in the illuminated manuscript Le Breviari d'Amor's (The Abstract of Love), attributed to Matfre Ermengau of Bezier dating to the late 1300s, are shown to turn the crank to produce night and day, They were subsequently replaced in another later image by a sage-like figure with an astrolabe in hand, creating and maintaining order.

Map from Ermengau of Bezier's Brevari d'Amor (The Abstract of Love) (1375 – 1400). The map depicts the Aristotlean-Ptolemaic cosmos where angels turn the crank to rotate the sublunary sphere perpetually to produce day and night.
/ The British Library
/
The British Library
Map from Ermengau of Bezier's Brevari d'Amor (The Abstract of Love) (1375 – 1400). The map depicts the Aristotlean-Ptolemaic cosmos where angels turn the crank to rotate the sublunary sphere perpetually to produce day and night.

Our evolving understanding is revealed by the changing depictions of our cosmic view. The Ptolemaic universe, with its earth-centric orderliness, was replaced by Copernicus's model, which reflected observations of the planets and placed the sun at the center of the known universe.

But acceptance of these transforming views is not straightforward, and opposition can be found, again, in maps. Take a 1651 map drawn by Giovanni Batista Riccioli. He depicts his own model in which most of the planets revolved around the sun while the sun itself revolved around the earth. The period's equivalent of today's peer-reviewed paper, maps became the currency of contestation, negotiation and dissemination of new ideas. This personal favorite contains an illustration in which Urania, the muse of astronomy, weighs these two maps to adjudicate between them. Ptolemy, meanwhile, is shown as a tired, old man relegated to the bottom of the frame along with his abandoned celestial map.

Urania weighs with scales the credibility of the Copernican system on the left against Riccioli's own adaptation of Brahe's model on the right. The scales in Riccioli's book predictably tilt in favor of his own theory wherein Mercury, Venus, and Mars orbit around the sun that in turn orbits around Earth, whereas Jupiter and Saturn remain on their Ptolemaic geocentric orbits.
/ Library of Congress
/
Library of Congress
Urania weighs with scales the credibility of the Copernican system on the left against Riccioli's own adaptation of Brahe's model on the right. The scales in Riccioli's book predictably tilt in favor of his own theory wherein Mercury, Venus, and Mars orbit around the sun that in turn orbits around Earth, whereas Jupiter and Saturn remain on their Ptolemaic geocentric orbits.

The quest for ever-better cosmic maps has continued. There are still momentous leaps in our comprehension of the cosmos and our place in it. First, the size of our universe grew, extending beyond our own galaxy with the astronomer Edwin Hubble's 1925 discovery that the Andromeda nebula lay outside and beyond the Milky Way. What's more, he detected that these other galaxies appeared to hurtle away from us — the farther away they were, the faster they traveled. Hubble's observations of the expanding universe unmoored us, rendering a radical, more complex and disorienting map.

Now, we know that these galaxies are not just trotting away but galloping, carried by the accelerating expansion of the universe, in turn driven by a mysterious repulsive force. Albert Einstein attributed this repulsion to the vacuum, the energy of space itself. Current observations estimate it has possibly dominated the activity of the universe for the past four billion years. This elusive force is dubbed dark energy — and with dark matter makes a powerful dark duo that dictates the fate and geometry of the cosmos.

Unseen directly, dark energy and dark matter show themselves through the effects that they exert on visible celestial objects. Dark matter tugs on stars in galaxies — and on galaxies in galaxy "clusters" — to make them whizz more quickly than if they were propelled merely by what we see. Dark matter also reveals its presence by dramatically bending light rays in the universe — "gravitationally lensing" the appearance of distant galaxies that we view through its veil.

Acting as nature's telescopes, these galaxy cluster lenses, replete with dark matter, bring into view some of the dimmest and farthest galaxies in the universe — ones that would otherwise be well beyond our reach with any instrument that we could ever build. With the exquisite resolution of the Hubble Space Telescope, we are able to find and map the locations of this dark component. Though we do not yet know the nature of dark matter, we have extremely detailed maps of it that might well lead us to better models, or better still, the elusive particle itself.

Our current maps also include everyone's favorite invisible entities: black holes, those objects that trap all light in their vicinity. Be they stellar-mass (some five to 10 times the mass of our sun) or super-massive (hundreds of thousands to billions of times the mass of our sun), black holes also reveal their presence only by their effects on others and how they mangle light, our cosmic messenger.

Yet another unseen domain was brought into view recently. In 2016, the Laser Interferometer Gravitational-Wave Observatory (LIGO) has allowed us to see two pairs of black holes directly, by capturing for the first time gravitational waves — invisible tremors in space time — emitted during their violent union. Gravity waves are an exciting prospect for a new age of exploration — and, in turn, for even more nuanced maps.

Our capacity to radically re-imagine the cosmos and our place in it remains alive and well.


Priyamvada Natarajan is a theoretical astrophysicist and professor in the departments of astronomy and physics at Yale University. Her first book titled Mapping the Heavens was published at the end of May by Yale Press.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Priyamvada Natarajan

You make NHPR possible.

NHPR is nonprofit and independent. We rely on readers like you to support the local, national, and international coverage on this website. Your support makes this news available to everyone.

Give today. A monthly donation of $5 makes a real difference.