How big is Black Pillar? | Scale of the Universe

The Black Pillar is a tower of cold gas and dust rising from the Eagle Nebula, a cloud where new stars are forming about 7,000 light-years from Earth. A light-year is the distance light travels in one year, about 9.46 trillion kilometers. The tower is about 9.5 light-years, or 90 trillion kilometers, tall from its base to its tip. The Hubble Space Telescope photographed it in 2004, and NASA and the European Space Agency (ESA) released the picture as "The Eagle has risen: stellar spire in the Eagle Nebula".

Size

ESA and NASA both give the tower's height as 9.5 light-years. That is the length of the column from the pedestal-like base at the bottom of Hubble's picture to the glowing clumps at its top.

The height depends on how far away the Eagle Nebula is. Astronomers work out a length like this from how long the object looks on the sky and how far away it is, so the height is only as certain as the distance. Both agencies put the nebula about 7,000 light-years away. The whole Eagle Nebula is far larger than the tower: NASA gives it a span of 70 by 55 light-years.

Size comparisons

The tower is a little more than twice the distance from the Sun to Proxima Centauri, the nearest star, about 4.2 light-years away.
It is more than twice as tall as the tallest of the Pillars of Creation, which is about 4 light-years long. The pillars stand in another part of the same nebula.
The Crab Nebula, the cloud left behind by a star that exploded, averages about 11 light-years across, a little more than the Black Pillar's height.
If the Black Pillar were shrunk to the height of Mount Everest, 8,849 meters (29,032 feet), the orbit of Neptune would be a circle about 90 centimeters (2.9 feet) across. Earth's orbit would be about 3 centimeters (1.2 inches) across.
The Eagle Nebula's longest span, 70 light-years, is about seven times the height of the tower.

How the tower is being shaped

The tower is being worn away by ultraviolet light from a group of massive, hot young stars off the top of Hubble's picture. The same starlight lights up the tower's rough surface. Streamers of gas boil off that surface, making the haze around the column. The tower stands out as a dark shape against the glow of more distant gas.

The top of the tower has lasted because the gas there is thicker. ESA compares it to dense brush in a field of prairie grass: a fire sweeps quickly through the grass but slows when it reaches the brush. The colors in Hubble's picture come from gas energized by the stars' ultraviolet light. The blue at the top is glowing oxygen, and the red lower down is glowing hydrogen.

Stars forming inside

Stars may be forming inside the tower. The bumps and fingers of material near its middle are places where stars are born, and each is roughly the size of the Solar System. Young stars there grew by feeding on the surrounding gas until light from the nearby star cluster uncovered them and cut off their supply.

The same light may also be starting new stars. It heats the gas at the top of the tower, and the heated gas expands and pushes against the colder, darker gas beneath it. Squeezed like this, the gas forms stars more easily. Hubble took the picture in November 2004 with its Advanced Camera for Surveys, and it was released in April 2005 to mark the telescope's 15th anniversary.