Dark Ages Radio Explorer facts for kids

The Dark Ages Radio Explorer (DARE) is a special spacecraft designed to orbit the Moon. Its main job is to study a mysterious time in the universe called the "Dark Ages."

DARE will look for faint radio signals from the very first hydrogen atoms. These signals will help scientists understand when the first stars began to shine and light up the universe. This period, known as the "Dark Ages," happened about 80 million to 420 million years after the Big Bang (the beginning of the universe).

By studying these signals, DARE hopes to find out how the first stars and black holes formed. It will also help us understand reionization, which is when the universe became filled with light. The mission might even give us clues about dark matter. DARE could also help develop telescopes on the lunar surface to explore planets around other stars. It was expected to launch around 2021 or 2022.

What Were the Dark Ages?

The "Dark Ages" were a time in the universe after it had cooled down enough for atoms to form, but before the first stars and galaxies were created. During this period, most of the matter in the universe was neutral hydrogen gas. There were no bright lights like stars or galaxies yet, so the universe was mostly dark.

Scientists want to observe this neutral hydrogen. They do this by looking for a special radio signal called the "21-cm hydrogen line." This signal comes from hydrogen atoms when their tiny parts, an electron and a proton, change their spin direction. This change releases a small burst of energy, which we can detect as a radio wave with a wavelength of 21 centimeters.

We can only see this signal when the hydrogen gas is at a different temperature than the cosmic microwave background (CMB). The CMB is like a faint glow left over from the Big Bang.

Why Study the Universe's Early Days?

The Big Bang created a very hot and dense universe. As it expanded, it cooled down. Eventually, tiny particles came together to form nuclei, and then atoms.

About 400,000 years after the Big Bang, the universe cooled enough for protons and electrons to combine and form neutral hydrogen atoms. At this point, the universe became "optically thin." This means that photons (light particles) could travel freely without bumping into matter. We still see these photons today as the cosmic microwave background (CMB). The CMB shows us that the early universe was very smooth and uniform.

After hydrogen atoms formed, the universe was mostly filled with this neutral hydrogen gas. Since there were no glowing stars or galaxies yet, this time is known as the "Dark Ages."

Scientists believe that over the next few hundred million years, gravity slowly pulled this gas together into denser areas. In these dense spots, the very first stars eventually appeared. This moment is called "Cosmic Dawn."

As more stars and the first galaxies formed, they released a lot of ultraviolet light. This light was strong enough to "re-ionize" the hydrogen gas, turning it back into charged particles. This period, a few hundred million years after Cosmic Dawn, is called the "Reionization era." It's a key event caused by the first galaxies.

Studying these early times helps us understand how the universe changed from a simple, dark place to the complex one we see today. Telescopes like the Hubble can see very far back in time, but DARE will look even further, into the true beginning of structures in the universe. DARE will make the first measurements of when the first stars and black holes were born.

DARE's Mission

DARE's goal is to measure the special 21-cm radio signal. It will observe signals from a time when the universe was between 80 million and 420 million years old (this is called a redshift range of 11 to 35).

DARE will orbit the Moon for three years. It will collect data from above the Moon's far side. This location is special because it's very quiet when it comes to human-made radio signals. This means DARE can hear the faint signals from the early universe without interference.

The spacecraft has a special science instrument. It includes three antennas that are good at picking up radio waves. It also has a receiver and a digital device to analyze the signals. These tools are very important for separating the weak 21-cm signal from other strong radio signals coming from space.

Other Similar Projects

Besides DARE, other projects are also trying to study the universe's early history. These include:

• The Precision Array for Probing the Epoch of Reionization (PAPER)
• The Low Frequency Array (LOFAR)
• The Murchison Widefield Array (MWA)
• The Giant Metrewave Radio Telescope (GMRT)
• The Large Aperture Experiment to Detect the Dark Ages (LEDA)