We are living in a wonderful time as space missions depart for the stars, the man begins to master the Moon, and robots become full members of crews. Still, some simple questions remain that we will address in today’s column with simple answers.
Why is it dark inside black holes?
Such mysterious space objects are complex on the one hand, and rather simple on the other.
Researcher Vyacheslav Dokuchayev explains that the term “black hole” is used to refer to a densely compacted massive object. Such an object may be made of several stars clumping together that, due to their small size, do not pass light. In scientific terms, the fact is that the escape speed on the surface of this body is greater than the speed of light, and therefore photons of light cannot escape.
Black holes are an important object for fundamental studies. Their study is moving forward thanks to the development of space research technologies. For example, in 2017, American scientists received the Nobel Prize for a discovery that helped to explore black holes. They discovered gravitational waves. Physicists then used sophisticated laser interferometers to record mergers of black holes that generate gravitational waves. These waves have been recorded, and the uniqueness of the signal suggests that only black holes can be the source of this waveform.
The global scientific community recognized the significance of the American scientists’ findings, and a year after their discovery, researchers were awarded the prize.
Our understanding of mysterious black holes has become more accurate over the past 40 years. This happened after the discovery of quasi-star objects or quasars. These are the most powerful emitters in the universe. They also comprise accreting black holes with masses millions and billions more than the Sun. They are located in the center of distant galaxies.
What color is the Sun?
In fact, the Sun is white, not yellow. This is because of its temperature. At 5780 kelvins, it makes the star shine with that hue of light.
A closer look will reveal other colors in the sky: colder stars are red, and hotter ones are blue. As soon as the sun's rays “touch” the Earth, their color changes to yellowish.
The sun emits all the colors of the visible spectrum.
That’s how it happens. Light particles known as photons are more difficult to scatter at the lower length of the visible electromagnetic spectrum (yellow, orange and red belong here as they have greater wavelengths) than photons of the upper part of the spectrum (violet, blue and green with shorter wavelengths). The Earth’s atmosphere passes longer waves from the yellow-red part of the spectrum, as if were “filtering out” light.
There is another explanation for the “yellowness” of the Sun. The tint is obtained due to contaminants in the atmosphere which enhance the scattering effect. That’s why over a desert with a clear and cloudless sky, our star appears white.
What happens at sunrise and sunset when the Sun “burns” with fiery hues?
It’s all about position. The Sun is closer to the horizon, so light has to penetrate through more atmospheric molecules. More photons of the blue-green spectrum are diverted by scattering, while low-energy yellow, red and orange photons remain on track.
The Sun can only be seen in its true color from the space where photons have nothing to interact with.
Why are the stars flickering?
Actually, flicker is not characteristic of the stars themselves. It happens because of the Earth’s atmosphere. The rays of stars must pass through it, and only then they can be seen by the inhabitants of the Earth. Above the turbulent gas shell of the planet through which we view the universe, there is no flicker of stars: all of them emit a smooth and stable light.
It is likely that many have seen individual objects fluttering on hot days when the soil is heated by the Sun strongly. The reason for that fluttering appearance is the same. The light from stars passes not through a homogeneous immovable environment but through gas layers of different temperature and different density. This atmosphere features many optical prisms, convex and concave lenses which endlessly change their positions. As they travel through such “mazes,” light rays undergo numerous deviations from their straight path, alternatively becoming concentrated and scattered. Therefore, both the brightness and color of the stars change every now and then.
This property of the atmosphere interferes with astronomers’ observations of the sky, so an important role is played by telescopes are located outside the Earth’s atmosphere. For example, Kepler and Hubble.
This is important because the removal of atmosphere, firstly, eliminates distortion and attenuation of light coming from stars, and secondly, it makes measurements more accurate. So, the Kepler telescope helped scientists discover many exoplanets that cannot be seen from Earth. Another important area of modern science that compensates for such atmospheric distortions is adaptive optics.
Photo on the homepage and on the page: Casey Horner / Photo bank Unsplash
