Black Holes Aid in Earth Navigation

Three large parabolic antennas tower against the sky as one approaches the gates of the Onsala Space Observatory, located south of Gothenburg. Perched on cliffs overlooking the sea, these antennas scan the cosmos.

Nearby, a massive structure resembling a giant golf ball stands beside a cluster of red buildings. A fourth enormous antenna, measuring 20 meters in diameter, is shielded by a lightweight fiberglass cover but has the capability to observe distant reaches of the universe.

Historically, astronomers relied solely on optical telescopes that captured light in wavelengths visible to the human eye. However, to truly comprehend the universe, it is essential to observe it across various wavelengths, explains the director of the Onsala Observatory, John Conway.

Upon entering the small airlock connecting the control room and the telescope, visitors find themselves in a room maintained at a slight overpressure to keep the protective dome inflated.

The telescopes at Onsala detect phenomena beyond the capabilities of human vision. The large parabolic antennas are designed to pick up radio signals from celestial objects located far from Earth.

They can identify magnetic fields and trace the presence of atoms and molecules, including hydrogen atoms, which constitute the majority of the universe's mass, Conway states.

The gigantic telescope inside the dome adjusts its focus every few seconds or minutes, switching between remote black holes located light-years away from Earth.

Amid the high-tech environment, there are also more practical amenities. Below the telescope, one can find sofas, grills, and various electronic devices.

The twin telescopes represent the observatory's latest advancements; the first was commissioned in 2017, while the larger 25-meter antenna has been operational since 1963.

Astronomer Robert Cumming points out a prototype receiver intended for the SKA Observatory in South Africa, which hangs on the wall.

At the Onsala Observatory, affiliated with Chalmers University of Technology, researchers are engaged in developing new technological solutions for telescopes worldwide and simultaneously exploring the cosmos.

This research, akin to the structure of the golf ball, has both terrestrial and astronomical implications. Astronomy was the first science to receive state support, as monarchs across Europe funded the establishment of observatories.

The purpose was not solely research; the star maps created by astronomers were strategically significant, aiding trade ships and military fleets in navigating the night sky.

This type of stargazing is known as optical astronomy, a practice with ancient roots. Historical accounts suggest that the Phoenicians navigated the Mediterranean using stars long before the birth of Christ.

The link between navigation and astronomy is indeed historic, and the work being conducted at Onsala is a continuation of this legacy. Rather than observing stars, researchers now utilize radio waves emitted by distant black holes, Conway adds.

This modern research field emerged in the 1930s, following successful attempts to study the universe through radio signals. Radio astronomy made its debut in Sweden in 1949 when Chalmers professor Olof Rydbeck acquired five military radar antennas left behind by German forces in Norway after World War II. These antennas were transported to scenic Råö, south of Gothenburg, laying the foundation for the Onsala Space Observatory.

While the original radar antennas have been replaced, the large 25-meter telescope erected in 1963 remains in use today. Utilizing this equipment, Rydbeck and his colleagues achieved a scientific breakthrough in 1973, becoming some of the first globally to observe molecules in space using radio emissions.

On a breezy February day, the 25-meter telescope and the two smaller twin telescopes stand tall. In their shadow lies the observatory's visitor center, where Cumming activates a monitor he often uses to engage school groups in discussions about astronomy.

The screen displays a list of distances from Onsala to various observatories worldwide--Germany, Hawaii, Australia--and a meter on the far right indicates how distances increase, seemingly in real-time, by a few nanometers at a time.

While this is merely an estimation, it illustrates a crucial point: the Earth's crust is not as stationary as it may seem underfoot. Continental plates gradually shift apart, creating new distances and reshaping the planet's surface over eons.

These changes, although imperceptible to the average person, occur at rates of several centimeters annually, significant enough to impact daily life.

In the control room, overlooking the dome's interior, computer monitors line two desks, accompanied by mismatched office chairs. Here, researchers prepare for the next round of observations, targeting thousands of black holes to be examined swiftly--both locally and at sister telescopes in other countries.

Today, the Onsala Observatory is part of several global networks. By allowing telescopes in different locations around the world to focus on the same radio source, researchers can extract valuable data.

When a wavefront approaches Earth, it is first detected by one telescope and then another, explains Rüdiger Haas, a professor in space geodesy, a field focusing on studying the Earth's surface using satellites and distant celestial objects.

Subsequently, the telescopes compare their results. Observing the same radio sources from different positions on the planet enables scientists to determine our actual location in the universe, how the Earth moves, and the distance to the black holes they are studying.

This is where astronomy intersects with everyday life. GPS systems struggle to differentiate between the movements of satellites and those of the Earth, Haas notes.

The mapping applications on smartphones utilize GPS signals from satellites orbiting the Earth. When entering an address, the app must not only display the route but also pinpoint the user's exact location with a small blip on the screen.

However, the Earth's surface is not static and is gradually changing. While satellites follow their orbital paths, the ground shifts slowly beneath them.

Without telescopes, GPS systems might function adequately for a few weeks, but eventually, they would "drift." They would lose track of the user's location on Earth, Haas explains.

Thus, data from Onsala and other observatories are essential for keeping global positioning systems updated regarding our whereabouts on both Earth and in the universe.

With impressive precision, particularly as the new telescope network, which includes the twin telescopes at Onsala, becomes fully operational.

Radio astronomers not only assist in calibrating GPS signals; their measurements of the Earth's rotational speed are crucial for determining when to introduce leap seconds to keep our daily rhythms synchronized.

We often claim that we can locate a point on the Earth's surface with centimeter-level accuracy, and with the new telescopes, we aim to achieve millimeter-level precision, although we have yet to reach that goal, Haas states.

He swiftly browses a list of what the observatories in the network are currently investigating. The screen illustrates black holes as simple red circles, the shapes they assume when observed from Earth. Haas pauses at one that appears nearly circular.

The radio emissions from this galaxy are nearly point-like, making it ideal for our studies, he explains.

This creates a coordinate on a star map, a nearly constant reference point in relation to Earth that can be used to ascertain our location in space and on Earth.

The Onsala Observatory, situated on Råö a few miles south of Gothenburg, benefits from land donated by Victor and Erna Hasselblad.

While astronomers may find these round points uninteresting, as they do not facilitate compelling research, they can be utilized for positioning purposes, Haas remarks.

Each day, telescopes can observe thousands of similar objects, focusing for mere seconds or minutes on each and mapping the universe, akin to the explorers of old.

Haas's work is described by Conway as applied astronomy, as it utilizes black holes for the benefit of humanity, while Conway's research is more abstract, centered on galaxy formation that requires analyzing radio signals that have traveled millions of light-years through space.

This research field is not always easy to justify to the public, even though it is vital for fundamental science in understanding the cosmos' interconnectedness.

People often question why we study black holes and what relevance they have to daily life. Yet, the fascinating aspect of science is its interconnectedness; it turns out that everything is linked. This can have practical applications, Conway adds.

He describes it as an exciting synergy. The same telescopes and technological solutions can be employed to enhance our understanding of the universe's origins and ensure that individuals do not get lost while traveling.

Currently, efforts are underway to apply radio astronomy to comprehend another pressing terrestrial issue: the impact of climate change.

Inside a room lined with shelves filled with binders and black plastic boxes, retired electrical metrology professor Gunnar Elgered is present. He mentions taking the opportunity to join colleagues for a traditional Swedish semla treat.

Elgered is focused on researching sea-level rise and atmospheric water formation. In this context, telescopes provide crucial data.

While the telescopes are designed to receive signals from black holes billions of light-years away, Elgered is more interested in phenomena occurring on Earth's surface.

Satellite measurements can help gauge sea levels not only along coastlines but also in the open ocean. Furthermore, radio signals traversing the Earth's atmosphere can offer insights into its gas composition.

We can measure water vapor in the atmosphere, a significant uncertainty in climate models, Elgered explains.

Water vapor contributes to the greenhouse effect, and as temperatures rise, more water evaporates, creating a self-reinforcing cycle. However, to what extent?

There may also be a counterbalancing effect: increased water vapor leads to more cloud formation, making the Earth appear whiter from space and reducing solar radiation reaching the surface. This is a challenging balance to quantify, he concludes before joining colleagues for refreshments.