If You Get Lost in the Universe, How Do You Get Back to Earth?

Maybe you’ve ever imagined, one day you’re lost far away outer space, far from the earth and the solar system. They all look the same, you can’t tell which is a galaxy or which is a star. From these stars you are also difficult to determine which is the sun. In the midst of the confusion, out of nowhere came an alien with his spaceship, generously offering a ride back to earth.
“Hubble Ultra Deep Field” image, containing 10,000 galaxies in the farthest reaches of the universe (credit: NASA)

You try to explain to the alien that you are from earth. You describe the earth and the sun with descriptions you remember. Earth is a blue planet with oceans, 1 AU from its star. Then you also explained that the sun is a G-class star surrounded by eight planets, as well as around the center of the Milky Way galaxy. The alien is confused, because all stars look the same, and almost all have planets, how to know which one is earth?

The universe looks the same from all directions

The universe is formed so that we can easily get lost. Stephen Hawking in his book A Brief History of Time once said “The universe looks the same no matter where you look at it.” There is no prominent part in this universe, and almost everything is identical and not special.

Wherever we stand in the universe, the natural landscape of the sky is relatively the same. That is, all galaxies almost resemble the Milky Way, and almost all stars resemble the sun. When there is no special uniqueness, a complete description of our sun becomes irrelevant, “The stars on my planet are like that too,” said the alien.

There is actually one solution to navigating in the void of the universe, and it was once used by NASA to pinpoint the position of the solar system via messages attached to Voyager. This message is deliberately aimed at aliens.

NASA uses pulsar map or a pulsar map to show where the sun is, in case aliens find it. First, let’s discuss what a pulsar is.

Pulsar, a dead star that becomes a beacon

Reporting from Space.com, pulsars are space objects that are very small (the size of a big city), but can have a mass more than the sun. Pulsar itself is an acronym for pulsating star, or a pulsating star.

The pulse comes from the blinking radio signal it produces. In the midst of the darkness of the universe, pulsars act like lighthouses in the dark sea at night. If our eyes can see the radio spectrum, and are sensitive enough, then we will be able to see objects at night that are blinking rapidly.

One of the famous pulsars is in the middle of the Crab Nebula. This pulsar is only about 30 kilometers in diameter, and ‘beats’ about 30.2 times per second.

The Crab Nebula captured by the Hubble telescope (credit: NASA)

Although the name is a pulsating star, the use of the word star itself is not quite right because pulsars are not stars. More precisely, pulsars are stellar corpses that form after a star ends its life in a supernova.

There is something special about this pulsar. Each pulsar is unique, there are properties that allow us to distinguish one pulsar from another. Characteristic (signature) is present at the pulsar’s rotational frequency. Reported by Space.com, the rotation frequency of pulsars ranges from zero point a few seconds, to hundreds of revolutions per second, and no pulsar has the same frequency.

Like getting lost in the middle of the city, you can think of this pulsar as “this 20-floor building is 200 meters to the north, while the intersection is only 50 meters to the west”. A marker or reference, whatever the term can be used as a reference for direction, and its nature can be used by many people who come from all directions.

Pulsar map on Voyager Golden Disc: plan for aliens

Pulsars as interstellar navigation are not new. NASA used it almost half a century ago on the Voyager and Pioneer probes. Hopefully, when intelligent aliens find the mission’s satellites somewhere in outer space, the aliens will know that the earth was the sender, as well as know where the earth is.

Voyager gold recording plate (credit: NASA/JPL)

Let’s talk about NASA’s message on Voyager first. Currently, Voyager 1 and Voyager 2 are the furthest man-made objects from Earth. Voyager 2 is more than 22 billion km from Earth and has long entered interstellar space.

On the body of the Voyager is a phonograph gold disc (called the Voyager Golden Record). Where in it are recorded images and music that NASA wants the aliens to see. On the cover of the disc, there are stripes motifs like the iconic fireworks. The image is called a pulsar map. Simply put, the picture is a plan for aliens to find us among the stars of the Milky Way. Scary or interesting?

When someday intelligent aliens find Voyager, researchers hope the aliens will receive the human message and know where it came from. Researchers believe aliens with space technology and knowledge can understand how to read the pulsar’s map. One of the originators of this idea was the famous astronomer and writer, Carl Sagan.

This map of pulsars in Voyager shows the relative position of the sun with the 14 closest pulsars. These pulsars can be identified based on their respective frequencies. Then how to read it?

Pulsar Map Caption on the Voyager Golden Disc (original image: NASA)

When we read a map, we should at least know which direction is north, some prominent objects, and know where we stand. In the case of a pulsar map, the ‘object stand out’ here is the pulsar itself. The images on the Voyager disk carry information in the form of the pulsar’s frequency, relative distance to the sun, the sun’s distance to the galactic center, and the pulsar’s distance to the ‘flat plane of the galaxy’ (galactic plane).

Pulsar Based Navigation: GPS but for exploring the galaxy

If humans have entered the technology that allows interstellar travel like warp drives in Star Trek, how do humans navigate like using GPS on earth? Actually it’s still the same. The concept of a pulsar map navigation map for exploring outer space has been further developed by researchers. This navigation system is named x-ray pulsar based navigation or timing (XNAV) or simply pulsar navigation.

Pulsar map version of the x-ray spectrum detected by the NICER instrument mounted on the ISS (credit: NASA)

This XNAV will help humans later when we have started exploring planets outside the solar system. By relying on pulsars that can be identified and matched against cataloged frequency and position data, the spacecraft can estimate its position. Maybe you’re a little confused, above it was said that pulsars produce radios, but now why suddenly x-rays?

Pulsars produce not only radio signals, but also x-rays, even gamma. Each of these spectra has different uses for researchers. The advantage of using x-rays to navigate is that the required detector is smaller than that used to detect radio signals.

Pulsars in addition to being excellent for human navigation in the universe, are also objects for researchers to find out how physics in solid objects (other than black holes) works. Pulsars, as a form of neutron star, are also responsible for the presence of heavy metals including gold in the universe. Pulsars have succeeded in becoming interesting and important objects in the universe.

So if one day you get lost in space, just show the Voyager pulsar map to the aliens who gave you a lift. The good thing is, even though aliens don’t understand human language, there is still a possibility that aliens can understand the pulsar map map that you show.

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