Hubble Space Telescope is currently the largest telescope in service, providing us the deepest looks off the unknown. In Hubble’s 29 years of service, many far away, many fainter, many younger galaxies and stars have been found and observed. But just like limits to any other observatory, Hubble too has limits and its hitting them.
Hubble has a great advantage of being a space telescope, the telescope doesn’t have to deal with the atmosphere and moving tiny particles that highly affect incoming light. But other than that, there are four other important factors that allow us to discover the faintest of the universe:
- The resolution
- The light gathering power
- The telescope’s field of view
- The wavelength range a telescope can scan
As of now, Hubble is great at all four. But with its recent discovering of the far away distant worlds and our need to probe the universe even farther, Hubble is highly unlikely to do better. It’s reaching its absolute limit.
Resolution is an important factor and deals in the amount of light a telescope can get into its primary mirror. Hubble here has a 2.4m mirror with diffraction-limited resolution of 0.05 arcseconds, allowing it to view visible light, ultraviolet light and near infrared light, with sensitivities ranging from a 100 nanometers to 1.8 microns.
Although it good and only a few other latest generation telescopes using state of the art adaptive optics systems, have been able to compete, there are not many ways to further improve it:
- Use even shorter wavelengths of light to fit in the same mirror size, further increasing the number of wavelengths.
- Increase the telescopes mirror size, thus increasing the number of wavelengths.
The light gathering power
This quality of the telescope deals in the collection of light over a greater period of time. Hubble being in space, doesn’t have to deal with the rotation of Earth or the atmospheric disturbance and is thus exceptionally good at this. The telescope can simply point and take an observation until done, also various observations can be added together to produce and even deep and long-exposure image with exceptional levels of details.
Field of View
Hubble with its eXtreme Deep Field has revealed around 5,500 galaxies in the regions measuring just 1/32,000,000 of the complete view. This observation was taken in 23 days and to further reveal the dimmer objects, 92 observation was set in place.
There is a catch here, Hubble is designed to go deep but not wide. It took more than 250 days of telescope time and a sticking of 7,500 exposures to get the deepest and widest view of the Universe. Hubble has been remarkable at this, but is now reaching its limits.
The Wavelength Range
Various objects in the universe emit various wavelengths of light, from ultraviolets to infrareds. Hubble can detect mostly all frequencies we know stars emit. But as light travels through space and with the universe expanding, even shorter wavelengths tend to be stretched by the expansion of space.
The Hubble Telescopes wavelength range sets the limit of how far back in the universe can we see — currently it is, when the universe was 400 million years old.
Hubble is reaching limits, the farthest galaxy to be discovered by Hubble is GN-z11, nothing farther than it has been discovered. But does it mean that this is the end, well no, universe stretches way beyond the GN-z11.
The future upcoming telescopes include the James Webb Space Telescope currently in works. This telescope other than being larger will operate at far cooler temperatures, ultimately enabling it to view longer wavelengths — upto 30 microns, compare that to the Hubble’s 1.8 microns.
Also, the James Webb telescope will be able to be see objects with far greater redshifts, meaning it will allow us to look back even farther — as far back as when the universe was 200 million years old. We will be able to see the formation of galaxies.